agent: Enable accepting and rejecting individual file changes from message editor (#32801)

Previously, you could only accept and reject all changes from a specific
file by checking that file out on a tab. Now, you can do that via the
message editor changes summary bar. The buttons appear as you hover over
the file item in the accordion.

Here's what it looks like:

<img
src="https://github.com/user-attachments/assets/8c0843d3-9bf1-4588-8b42-4cd8d0798a68"
width="500" />

Release Notes:

- agent: Enable accepting and rejecting individual file changes from
message editor.
c35f22dde0Danilo Leal committed on 6/16/2025, 2:28:37 PM· committed by GitHubparentfceba6c
1 file changedLine totals unavailable