GitLab

We remove some arguments that are rarely used or 
used just to simplify setups on specs.

Modified Mentionable#create_new_cross_references method 
we don’t need to calculate previous references to avoid the 
duplication because we do that at database level when 
creating references extracted from the current entity state.

MergeRequests won’t create cross_references for commits that are included so we change a spec to use a different merge request to make references to commits to other branches

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Caching is now always enabled when rendering attributes as there's no
reason to not cache them. The method Mentionable#all_references has also
been modified to take an optional Gitlab::ReferenceExtractor instance to
allow other code to create one and re-use it between multiple calls.

Fixes #14002

It now accounts for models that have changed but have already been
persisted, such as when called from an UpdateService.

Closes #1773

Fixes #1778

Except for Note, which still overrides it.

There's a lot of code in the Note model that only deals with creating
system notes, so we're going to split that into its own class.