Improve PR validation Azure DevOps pipeline process. (#4775)

* Move old PR + CI definition into CI-only file.
  - Make way for the new PR validation build def
  - Update triggers to only be for CI
- Now documented more completely.
- simplified steps to run, and adding new steps should be straightforward.
- Removed tests from PR validation to speed it up (Windows system tests are really the big ones)
- Fix some unit tests

Author: d3r3kk

build/ci/vscode-python-ci.yaml

@@ -0,0 +1,63 @@
+# CI definition only
+pr: none
+
+# CI build for merges to master and release.
+# Note: We are 'batching' builds at the moment. This will mean only one CI build
+#       will be triggered. If we find the resources available, turn off batching
+#       as it is nicer to have feedback on each and every merge.
+trigger:
+  batch: true
+  branches:
+    include: [ 'master', 'release' ] # branches that will trigger a CI build
+  paths:
+    exclude: [ '/news', '/.vscode' ] # file paths which will not trigger a build
+
+jobs:
+
+- template: templates/compile-and-validate.yml
+  parameters:
+    name: 'Prebuild'
+    pool:
+      name: 'Hosted Ubuntu 1604'
+    UploadBinary: true
+    Platform: 'Linux'
+
+
+- template: templates/virtual_env_tests.yml
+  parameters:
+    Platform: 'Windows'
+    pool:
+      name: 'Hosted VS2017'
+
+- template: templates/virtual_env_tests.yml
+  parameters:
+    Platform: 'Linux'
+    EnvironmentExecutableFolder: 'bin'
+    pool:
+      name: 'Hosted Ubuntu 1604'
+
+- template: templates/virtual_env_tests.yml
+  parameters:
+    Platform: 'macOS'
+    EnvironmentExecutableFolder: 'bin'
+    pool:
+      name: 'Hosted macOS'
+
+- template: templates/test-phase-job.yml
+  parameters:
+    pool:
+      name: 'Hosted VS2017'
+    Platform: 'Windows'
+
+- template: templates/test-phase-job.yml
+  parameters:
+    pool:
+      name: 'Hosted Ubuntu 1604'
+    Platform: 'Linux'
+
+- template: templates/test-phase-job.yml
+  parameters:
+    pool:
+      name: 'Hosted macOS'
+    Platform: 'macOS'
+