Diff note

What does this MR do?

• convert diff_note_avatar to Single File Component

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

• component needs some more complete tests. @click.native handler wasn't being triggered, and there is a still a bunch of jquery events and dependencies in there that I don't know what to do with

Why was this MR needed?

for diff components to be used in https://gitlab.com/gitlab-org/gitlab-ce/issues/38178

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
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?