Annotation activity enhancement poc

[ConradJChan]

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Draft for Annotation activity card enhancements.

Few high level callouts:

• Moved the padding for each activity feed item from the li to a mixin applied to each card so that the annotation card can be full width now that it is interactive
• Moved the Annotation link inline with the timestamp but had to use a FormattedMessage of on with some margin on each side to provide the adequate spacing to join the timestamp with the annotation link. Open to suggestions if there's a better approach
• To avoid excessive preventDefault and stopPropagation handling of events within the annotation card, I introduced a concept of isInteractive so that under certain conditions (version is unavailable, the overflow menu is open, or the comment is being edited) the interactivity is removed

This Draft PR is for reference and separate PRs will be broken out for review

[ConradJChan]

Added a gif