Builds on top of #46735

This PR refines the design for the discarding partial edits UX. When the user interrupts a generation midway through an edit, the UI will show a knockout warning icon in the file icon as well as a trash icon button to clean up/restore the file to its original content. Then, as soon as you click on that button, the file gets reverted and the button is gone. Here's the result:

In the video, I show these scenarios:

1. Interrupting an edit while there isn't yet a revealed diff: in this case, there's no need to expose a "discard interrupted edits" button; no edits have actually been applied yet
2. Interrupting an edit midway through it: this is the key UX here, where we want the quick button to revert the file back to the state before the interrupted edit
3. Trying to perform an edit while with a dirty file: this PR doesn't touch this state but thought of illustrating in the video as an additional error state

Release Notes:

• Agent: Improved the UX for discarding partial edits by allowing the user to quickly restore the file to its original content.