Support filtering the files view to only show files with comments

[jsoref]

• As noted in Comments (119) + There are no comments in this workspace yet. after restarting extensions vscode#252168, I have a PR with a sizable number of comments spread across some sizable number of files, but it's a fairly small subset of all files in the repository.

I'd like to be able to filter the Pull Requests pane to only show files with comments. Currently, I have:

And this comments pane:

Sure, I could highlight the first file in the comments pane, and then press the left arrow and then the down arrow and alternate through left and down until I got to the end, but it's fairly painful, and I don't get access to the pretty file hierarchy: