Refer to unnamed constructors in doc comments with '.new'

Cleanup for dart-lang/dartdoc#3531

This makes these comment references more idiomatic, I think
more readable, and supports dropping the leading `new ` syntax
in doc comments.

Change-Id: Id832ad14d9ea08fe03fe3125065755f49b1b93ed
CoreLibraryReviewExempt: doc comment only change
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330683
Reviewed-by: Devon Carew <[email protected]>
Reviewed-by: Lasse Nielsen <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

sdk/lib/convert/convert.dart

@@ -125,7 +125,7 @@
 /// The converter finds characters that are significant in HTML source and
 /// replaces them with corresponding HTML entities.
 ///
-/// Custom escape modes can be created using the [HtmlEscapeMode.HtmlEscapeMode]
+/// Custom escape modes can be created using the [HtmlEscapeMode.new]
 /// constructor.
 ///
 /// Example:

sdk/lib/convert/html_escape.dart

@@ -36,7 +36,7 @@ const HtmlEscape htmlEscape = HtmlEscape();
 /// All modes require escaping of `&` (ampersand) characters, and may
 /// enable escaping of more characters.
 ///
-/// Custom escape modes can be created using the [HtmlEscapeMode.HtmlEscapeMode]
+/// Custom escape modes can be created using the [HtmlEscapeMode.new]
 /// constructor.
 ///
 /// Example:

sdk/lib/core/uri.dart

@@ -26,7 +26,7 @@ const String _hexDigits = "0123456789ABCDEF";
 
 /// A parsed URI, such as a URL.
 ///
-/// To create a URI with specific components, use [new Uri]:
+/// To create a URI with specific components, use [Uri.new]:
 /// ```dart
 /// var httpsUri = Uri(
 ///     scheme: 'https',

sdk/lib/isolate/isolate.dart

@@ -68,7 +68,7 @@ class IsolateSpawnException implements Exception {
 /// The `Isolate` object provided by a spawn operation will have the
 /// control port and capabilities needed to control the isolate.
 /// New isolate objects can be created without some of these capabilities
-/// if necessary, using the [Isolate.Isolate] constructor.
+/// if necessary, using the [Isolate.new] constructor.
 ///
 /// An `Isolate` object cannot be sent over a `SendPort`, but the control port
 /// and capabilities can be sent, and can be used to create a new functioning