When following a link to a particular line ("/example.txt$12"), scroll to that line

Summary:
Depends on D19349. Ref T13105. This was the behavior in Diffusion before with a little hard-coded snippet.

Remove that snippet ("diffusion-jump-to") and add a more general-purpose snippet to SourceView.

This is a tiny bit hacky still (and probably doesn't work quite right with Quicksand) but gets things working again and works in all of Files, Paste, and Diffusion.

Test Plan: Followed links to particular lines in Paste, Files and Diffusion; got scrolled to the right place.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13105

Differential Revision: https://secure.phabricator.com/D19350