Markdown reference autocomplete inputs unneeded backslash

The following should be 1:1 with no strange characters being injected from the user perspective:

The reason https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18051 is implemented makes sense from a technical perspective, but not when advocating the user. We should look for a solution that solves it from both perspectives. Is there a way to hide it perhaps and make it invisible from the user's perspective?

This happens to all references that contain text: emojis (:arrow\_double\_down:), usernames (@julie\_manalo), labels, milestones (%"Next 3\-4 releases").

Currently, we also escape dashes (-). gitlab-ee!8936 adds autocomplete with namespaced issues / MRs. So my-project-name#123 becomes my\-project\-name#123 when a dropdown option is selected.