Render file patches with a decorated Editor #1512
Use decorations within an Atom TextEditor element to implement a file patch item. This should get us improved performance for large diffs, editable diff support, and open the path for multi-file diff views like a commit or pull request pane.
Just to set proper expectations, I'll likely need to pause and resume this a few times before it lands. Don't worry, I won't forget about it
Concurrent with review
Fixes #1502. ...Eventually