This PR includes design tweaks to elements involved on the "edit files"
flow: the bar that appears above the message editor, buttons on the
multibuffer hunks, adding keybindings to the "Review Changes" button,
etc.

<img
src="https://github.com/user-attachments/assets/4bff883a-c5c4-443e-8bf5-d98f535c83ce"
width="750" />

Release Notes:

- N/A