Use JavaScript tooltips for mentions

## What does this MR do?

- use JavaScript tooltips instead of plain title for mentions (issue, merge request, snippet, user, group, commit, commit range, milestone)

## Why was this MR needed?

JavaScript tooltips look nicer and can wrap.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5261#note_13106713, fixes #21500

See merge request !5301

Do not look up commit again when it is passed to RelativeLinkFilter

## What does this MR do?

Use `context[:commit]` in RelativeLinkFilter instead of looking up commit using `context[:ref]`.

## Why was this MR needed?

Even though the commit object was already passed, unnecessary I/O is done to retrieve the commit object.

## What are the relevant issue numbers?

Fixes #20026

See merge request !5455

Enable some Rubocop cops related to new lines

## What does this MR do?

This MR enabled two additional Rubocop cops:

Keeps track of empty lines around block bodies.  
`Style/EmptyLinesAroundBlockBody`

Keeps track of empty lines around method bodies.  
` Style/EmptyLinesAroundMethodBody`

See merge request !5637