Improve Repository Sync (with new SystemHook)

Closes #1463 and #1493

See merge request !1789

Fix slash commands detection in comments

See merge request !1876

Fix flickering of system notes -- EE merge edition

Closes gitlab-ce#32087

See merge request !1873

Use new Commit#raw_deltas method

See merge request !1854

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/32087

Easy reproduction:

 1. Edit an issue title
 1. Notice the system note added
 1. Switch to another tab and back (to fire the polling immediately)
 1. Notice the flicker (without this fix)

[EE] Resolve "Use consistent style for trailing commas"

See merge request !1796

Make all Serializers receive `current_user` instead `user` [EE]

See merge request !1869

Port of 32077-pipeline-graph-margins to EE

See merge request !1867

Use the EnforcedStyleForMultiline: no_comma option.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Use the EnforcedStyleForMultiline: no_comma option.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Feature availability check using feature list AND license addons

See merge request !1851

Fix icons path and mappings

See merge request !1862

CE upstream

Closes omnibus-gitlab#2234 and gitlab-ce#31271

See merge request !1837

This reverts commit 8785aa64.

Fix Timecop not unfreezing after spec

Closes #2362

See merge request !1847