docs: Add project panel's undo and redo documentation (#60191)

# Objective

Update the Project Panel's documentation to document which operations
support undo and redo behavior so it's easier for users to discover this
feature.

This Pull Request should stay in draft and only be merged after both
https://github.com/zed-industries/zed/pull/59709 and
https://github.com/zed-industries/zed/pull/59595 are merged, as
documentation mentions behavior that is being updated in both Pull
Requests.

Release Notes:

- N/A
95106f9cdeDino committed on 7/28/2026, 12:27:24 PM· committed by GitHubparent8780e3a
1 file changedLine totals unavailable