Credit: [@Musisimaru](https://gitlab.com/Musisimaru) (originally
introduced in
[!229](https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/merge_requests/229))

When we dispose commentController, all its therads will get disposed
automatically. We don't ever need to call dispose outside of the
GitLabCommentThread.

VS Code keeps the case. I.e. it  correctly replaces
even getWorkspaceFolders.

The only places where we didn't replace the string were when
we were using the VS Code API (vscode.workspace.workspaceFolders).

This is to be reverted in the next MR. This disabling is used instead of
a feature flag. Now the preliminary refactoring can be reviewed
separately.

If the comment changed on the server, but the extension still
shows the old version, we'll prevent the extension from overriding
the server's latest version. We'll warn the user that the
comment has changed since they last saw it.

Introduce startEdittingComment and cancelEdittingComment
commands that will open and close the VS Code comment
text area. The cancel command also resets the comment body
to the value retrieved from the API.

This is marked as refactor, because we don't want this commit to have
a line in the changelog. It's an uncomplete feature.

All logic related to creating vscode.CommentThread and
setting the correct properties has been extracted to one class.

This class will be responsible for resolving threads in the future.