Diff comment button debounce

What does this MR do?

Debounce the show, delay the hide and return early as possible for performance

Debounces the rendering of the comment button when mouseover a diff line.

Delays the hiding of the comment button when mouseleave a diff line.

Returns as early as possible during the rendering/showing/hiding of the comment button to reduce wasted computation.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/30404