[webview_flutter] Extract WKWebView implementation into a separate package (flutter#4345)

* Setup webview_flutter_wkwebview package.

Creates a new `webview_flutter_wkwebview` directory and adds
the following meta-data files:
- `AUTHORS`: copied from the `webview_flutter` package and added my name;
- `CHANGELOG.md`: new file adding description for release 0.0.1;
- `LICENSE`: copied from the `webview_flutter` package;
- `README.md`: new file adding the standard platform implementation
  description;
- `pubspec.yaml`: new file adding package meta-data for the
  `webview_flutter_wkwebview` package.

* Direct copy of "iOS" folder.

A one to one copy of the `webview_flutter/ios` folder to
`webview_flutter_wkwebview/` using the following command:
```
cp -R ./webview_flutter/ios ./webview_flutter_wkwebview/
```

* Rename .podspec file to match package name.

For the Cocaopod package to be registered correctly the .podspec file
name needs to match the name of the Flutter package.

* Direct copy of WKWebView specific .dart files.

Copied the WKWebView specific .dart files over from the
`./webview_flutter` package.

* Modify .dart code to work with new platform_interface.

Make sure the `CupertinoWebView` widget extends the `WebViewPlatform`
class from the `webview_flutter_platform_interface` package correctly by
accepting an instance of the `JavascriptChannelRegistry` class.

* Direct copy of the `webview_flutter/example` app.

This commit makes a direct copy of the `webview_flutter/example` app to
the  `webview_flutter_wkwebview` package. After the copy the `example/android`
folder is removed as it doesn't serve a purpose in the WKWebView specific
package. Commands run where:
```
cp -R ./webview_flutter/example ./webview_flutter_wkwebview/
rm -rf ./webview_flutter_wkwebview/example/ios
```

* Update example to WKWebView specific implementation.

This commit updates the example App so it directly implements the
WKWebView specific implementation of the webview_flutter_platform_interface.

* Update integration tests.

Updated the existing integration tests (copied from webview_flutter
package) so they work correctly with the implementation of the
webview_flutter_wkwebview package.

Co-authored-by: BeMacized <bodhimulders@bemacized.net>

* Fix iOS UI tests.

This commit resolves failing UI tests and ensures the `Publishable` task
is green.

* Point to existing documentation URL

Update the documentation URL in the
`ios/webview_flutter_wkwebview.podspec` file to point to a valid
location. The `https://pub.dev/packages/webview_flutter_wkwebview`
package doesn't exists until this PR is published. However the `pod lib
lint` step in CI is failing if the URL doesn't exist yet.

* Split helper classes from main example widget.

Move the `WebView` and related `WebViewController` classes from the
main.dart into a separate web_view.dart file.

* Updated version numbers as suggested in review.

Updated the version of the plugin to the version of webview_flutter
package (2.0.13).

Also updated the Dart and Flutter versions to respectively 2.14.0 and
2.5.0.

Co-authored-by: BeMacized <bodhimulders@bemacized.net>

Author: 2 people

packages/webview_flutter/webview_flutter_wkwebview/AUTHORS

@@ -0,0 +1,67 @@
+# Below is a list of people and organizations that have contributed
+# to the Flutter project. Names should be added to the list like so:
+#
+#   Name/Organization <email address>
+
+Google Inc.
+The Chromium Authors
+German Saprykin <saprykin.h@gmail.com>
+Benjamin Sauer <sauer.benjamin@gmail.com>
+larsenthomasj@gmail.com
+Ali Bitek <alibitek@protonmail.ch>
+Pol Batlló <pol.batllo@gmail.com>
+Anatoly Pulyaevskiy
+Hayden Flinner <haydenflinner@gmail.com>
+Stefano Rodriguez <hlsroddy@gmail.com>
+Salvatore Giordano <salvatoregiordanoo@gmail.com>
+Brian Armstrong <brian@flutter.institute>
+Paul DeMarco <paulmdemarco@gmail.com>
+Fabricio Nogueira <feufeu@gmail.com>
+Simon Lightfoot <simon@devangels.london>
+Ashton Thomas <ashton@acrinta.com>
+Thomas Danner <thmsdnnr@gmail.com>
+Diego Velásquez <diego.velasquez.lopez@gmail.com>
+Hajime Nakamura <nkmrhj@gmail.com>
+Tuyển Vũ Xuân <netsoft1985@gmail.com>
+Miguel Ruivo <miguel@miguelruivo.com>
+Sarthak Verma <sarthak@artiosys.com>
+Mike Diarmid <mike@invertase.io>
+Invertase <oss@invertase.io>
+Elliot Hesp <elliot@invertase.io>
+Vince Varga <vince.varga@smaho.com>
+Aawaz Gyawali <awazgyawali@gmail.com>
+EUI Limited <ian.evans3@admiralgroup.co.uk>
+Katarina Sheremet <katarina@sheremet.ch>
+Thomas Stockx <thomas@stockxit.com>
+Sarbagya Dhaubanjar <sarbagyastha@gmail.com>
+Ozkan Eksi <ozeksi@gmail.com>
+Rishab Nayak <rishab@bu.edu>
+ko2ic <ko2ic.dev@gmail.com>
+Jonathan Younger <jonathan@daikini.com>
+Jose Sanchez <josesm82@gmail.com>
+Debkanchan Samadder <debu.samadder@gmail.com>
+Audrius Karosevicius <audrius.karosevicius@gmail.com>
+Lukasz Piliszczuk <lukasz@intheloup.io>
+SoundReply Solutions GmbH <ch@soundreply.com>
+Rafal Wachol <rwachol@gmail.com>
+Pau Picas <pau.picas@gmail.com>
+Christian Weder <chrstian.weder@yapeal.ch>
+Alexandru Tuca <salexandru.tuca@outlook.com>
+Christian Weder <chrstian.weder@yapeal.ch>
+Rhodes Davis Jr. <rody.davis.jr@gmail.com>
+Luigi Agosti <luigi@tengio.com>
+Quentin Le Guennec <quentin@tengio.com>
+Koushik Ravikumar <koushik@tengio.com>
+Nissim Dsilva <nissim@tengio.com>
+Giancarlo Rocha <giancarloiff@gmail.com>
+Ryo Miyake <ryo@miyake.id>
+Théo Champion <contact.theochampion@gmail.com>
+Kazuki Yamaguchi <y.kazuki0614n@gmail.com>
+Eitan Schwartz <eshvartz@gmail.com>
+Chris Rutkowski <chrisrutkowski89@gmail.com>
+Juan Alvarez <juan.alvarez@resideo.com>
+Aleksandr Yurkovskiy <sanekyy@gmail.com>
+Anton Borries <mail@antonborri.es>
+Alex Li <google@alexv525.com>
+Rahul Raj <64.rahulraj@gmail.com>
+Maurits van Beusekom <maurits@baseflow.com>

packages/webview_flutter/webview_flutter_wkwebview/CHANGELOG.md

@@ -0,0 +1,3 @@
+## 2.0.13
+
+* Extract WKWebView implementation from `webview_flutter`.

packages/webview_flutter/webview_flutter_wkwebview/LICENSE

@@ -0,0 +1,25 @@
+Copyright 2013 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/webview_flutter/webview_flutter_wkwebview/README.md

@@ -0,0 +1,11 @@
+# webview\_flutter\_wkwebview
+
+The Apple WKWebView implementation of [`webview_flutter`][1].
+
+## Usage
+
+This package is [endorsed][2], which means you can simply use `webview_flutter`
+normally. This package will be automatically included in your app when you do.
+
+[1]: https://pub.dev/packages/webview_flutter
+[2]: https://flutter.dev/docs/development/packages-and-plugins/developing-packages#endorsed-federated-plugin

packages/webview_flutter/webview_flutter_wkwebview/example/.metadata

@@ -0,0 +1,8 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 1e5cb2d87f8542f9fbbd0f22d528823274be0acb
+  channel: master

packages/webview_flutter/webview_flutter_wkwebview/example/README.md

@@ -0,0 +1,8 @@
+# webview_flutter_example
+
+Demonstrates how to use the webview_flutter plugin.
+
+## Getting Started
+
+For help getting started with Flutter, view our online
+[documentation](https://flutter.dev/).