Partially addresses #47424.

Also added relevant specs and refactored to_references in a bunch of places to be more consistent.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

This method used to call strip! on input strings which will mess with
the strings if they're re-used or frozen.

These methods are called quite often in loops so by memoizing their
output we can reduce timings a bit.

This is the git default and will help to prevent false positive matches.

Closes #12706

We only want them shortened by the filter, which calls to_s

Now there is a single source of information for which attribute a model
uses to be referenced, and its special character.