Move the comment functions from EditorCommandHandlers to EditorCommentHandlers

[TomMalbran]

EditorCommandHandlers, is getting big, and will keep growing and the the test file is huge, making it hard to work with and to test the tests, so I would suggest to move all the comment functions into a new file EditorCommentHandlers and the tests too since those are what are using most of the space right now.

[gruehle]

Reviewed -- good suggestion!

[peterflynn]

Two suggestions:

1. Also split EditorCommandHandlers-test, which is 4x even more huge
2. Instead of EditorCommentHandlers, how about something like ToggleComment or CommentUncomment? The "Editor"/"Handler" prefix/suffix are pretty generic and don't seem that necessary.

[peterflynn]

We should wait for #3060 and possibly the token stream stuff to land before doing this -- otherwise the merge conflicts will be a nightmare.

[TomMalbran]

1. Yes, the split would split the test files too following the same split as the EditorCommandHandlers, leaving all the comment tests in one test file and the rest in the original file.
2. I like the ToggleCommentHandlers name, CommentUncommentHandlers is a bit too long, or you referring without the handlers suffix in the name?