Test: GitHub Pull Request extension improvements

[rebornix]

Ref: microsoft/vscode-pull-request-github#544

Complexity: 4

• Windows @alexr00
• Linux @Tyriar
• macOS @sbatten

Authors: @rebornix, @RMacfarlane

Within this iteration, we made following major improvements to VSCode's commenting support and the GitHub Pull Request extension

• You can now merge pull request in the description view of a pull request. Please note that we don't support CI checks or merge with squash, etc.
• We support multiroot workspace now
• You can now edit and remove comments in both VSCode editor and the description view of a pull request
• We have caching support for pending comments in both VSCode comment widget and the description view. When you are editing a comment, switch to another editor (for example in the same editor group) and then come back, the pending comments should still be there.

Please test the latest version in the marketplace, which is 0.2.2

This repo can be used to test against.