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

The method Ability.issues_readable_by_user takes a list of users and an
optional user and returns an Array of issues readable by said user. This
method in turn is used by
Banzai::ReferenceParser::IssueParser#nodes_visible_to_user so this
method no longer needs to get all the available abilities just to check
if a user has the "read_issue" ability.

To test this I benchmarked an issue with 222 comments on my development
environment. Using these changes the time spent in nodes_visible_to_user
was reduced from around 120 ms to around 40 ms.

Signed-off-by: Rémy Coutable <remy@rymai.me>

Handle videos in:
- MD preview in notes: commit, issue/MR, MR diff
- New notes in: commit, issue/MR, MR diff
- Persisted notes in: commit, issue/MR, MR diff

Signed-off-by: Rémy Coutable <remy@rymai.me>