Add comment summary to the link's tooltip when the link points to a comment

Problem to solve

In a single discussion thread (for example, in an issue or a merge request), users often link to other comments within the thread to provide context. However, the tooltip of the link only includes the thread's title, which is not very useful when the link points to a comment in the same discussion:

Proposal

Add a summary of the comment (i.e., the first x words of the comment) to the tooltip to provide more relevant context.

Intended users

gitlab-ce~9335216

Further details

Currently, clicking a link to a comment within the same discussion doesn't reload the page, so the workaround isn't too painful - just click the link, read the comment, and click the back button to jump back to the previous scroll position.