Edit: Support opening a separate diff and improve diff editing

Description

This PR:

Allows opening a full diff via "Open Diff". With additional functionality for reverting specific lines etc.
- Note: We have to "accept" the task when we do this, this is so we don't have have a duplicate diff in this view from the inline diff and the separate diff. We could try to remove the inline-diff when opening this, and re-add when closing it, but that would spam the users' undo/redo stack, and likely lead to bugs keeping everything in sync
Improves functionality for editing the inline diff like it is just text