Backport panels.scss styles from EE

See merge request !12206

Add table for files in merge request diffs

See merge request !12047

Show private subgroups if member of parent group

Closes #32135

See merge request !11764

Call Capybara.reset_sessions! before block_and_wait_for_requests_complete

Closes #33779

See merge request !12224

This adds an ID-less table containing one row per file, per merge request
diff. It has a column for each attribute on Gitlab::Git::Diff that is serialised
currently, with the advantage that we can easily query the attributes of this
new table.

It does not migrate existing data, so we have fallback code when the legacy
st_diffs column is present instead. For a merge request diff to be valid, it
should have at most one of:

* Rows in this new table, with the correct merge_request_diff_id.
* A non-NULL st_diffs column.

It may have neither, if the diff is empty.

Rename "Slash commands" to "Quick actions"

Closes #27070

See merge request !11811

Remove issuable drag and drop and sorting from milestone view

Closes #20900

See merge request !11950

Add missing bottom border to blame age legend

Closes #33739

See merge request !12205

Missing translations for the project & repository pages.

Closes #33420

See merge request !12052