Test new comment api

[rebornix]

Refs: #68020

• any @joaomoreno
• any @sbatten

Authors: @rebornix, @RMacfarlane

Complexity: 4

GH PR extension has been using the proposed commenting api for more than half a year. Based on the lessons we learnt from dog fooding in GH PR, we refactored the api to be more SCM like and it's pretty close to what we imagine a generic but powerful enough commenting api should look like. If you are interested in the problems we ran into and our design decisions, please read #68020.

Right now the new commenting api and the legacy one are both in vscode.propsed.d.ts as we don't want to break any other extension using the legacy api immediately. So to get familiar with the API

1. Read Microsoft/vscode-extension-samples/blob/rebornix/.../vscode.proposed.d.ts. The api names should be self explanatory and jsdocs can help also.
2. Play with sample https://github.com/Microsoft/vscode-extension-samples/tree/rebornix/commentcontroller/comment-sample

You don't need to create a comment controller as complex as GH PR but please at least test

• Comment thread creation/disposal
• Comments update
• Customize actions on Comment Widget by Comment.acceptInputCommand and Comment.additionalCommands

Please provide feedback on the api, sample and docs/comments.

[sbatten]

I wanted to add a Delete Thread button, but the only way I could do that was by adding it to additional commands which requires the user to hit Reply... first. I think that's a little weird.