Fixes #3319

Instead of making complex query selectors this approach just filters out elements that shouldn't be targetable.

I mainly tested this code with use cases described in the issue, so if there are any other edge case I didn't consider please let me know.

Hidden conversations in Files tabs are "focused"

For this now any .js-minimizable-comment-group is ignored if if it is minimized.
I tested this with in #3242 (files), now only the files are targeted.
For me the comments also where hidden (and not visible when targeted) without pressing i first, so I handled both scenarios.

PR reviews are skipped

Targetable #pullrequestreview-{id} elements are now only targetable if they contain a message.
PR reviews with a message also contain a targetable element with #pullrequestreview-{id}-body-html.

So now pressing j on this issue comment skips the two messageless review comments and goes to the next review with a message below.

I noticed some problems with the .filter() approach because we might filtered out the current targeted element.
So e.g. if a messageless review is targeted, pressing j will jump to the first targetable element.
A better approach might be to target the next/previous targetable element instead.

Happy for any feedback on this, or if there are any other issues/use cases where this code doesn't work 😄