Add feature to toggle visibility of inline Check annotations on Files tab #3431

When a Check run adds annotations to files in a PR, they take up quite a lot of space on the Files tab. There doesn't currently appear to be any way to dismiss, collapse, or otherwise hide these annotations.

It would be nice to have a feature that has annotations collapsed by default, with the option to expand them individually (or all, via Alt-click), and then collapse them again.

Example PR with annotations: https://github.com/XiongKezhi/codingstyle/pull/4/files#diff-835eeb0e6f1f24bdcb7fb2ec14495a29

Screenshot from that PR: (the icon placed waaay over on the top-right of the annotation just links to the Checks tab; I can't see any option to hide the annotation)

Potential mockup:

I guess that actually dismissing annotations should probably be a GitHub-native feature, similar to the "Viewed" checkbox for files. But either way, it would be nice to to make diffs readable when faced with annotations.