Add command to manually trigger a refresh/rescan of folders

[auwi-nordic]

Closes #29598

This may also help a bit with #20849 in the cases where users can do a folder refresh instead of a reload to solve their workspace issues.

This adds both a project panel context menu "Refresh Folders" which refreshes the hierarchy below the chosen folder, and a command "workspace: refresh folders" which refreshes everything in the current window.

Should work for remote ssh sessions as well. Tested locally and on remote workspaces on MacOS.
Checked that it functions as workaround for #35173

I have very little experience with Rust and the Zed codebase, so someone more experienced should review the changes thorughly. Feature was implemented with the help of Claude agent, but did some iterations and manual changes to tidy up things.

Feature name is inspired by the Sublime "Project: Refresh Folders" command, which does something similar.

Release Notes:

• Add command to manually trigger a refresh/rescan of folders

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[auwi-nordic]

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[auwi-nordic]

Some things I'm uncertain about, which may need tweaking

1. I don't know if adding a new remote request type, but it didn't seem I was able to re-use ScanRequest or PathPrefixScanRequest
2. I'm not sure about the placement of the context menu item. At the bottom seems sensible, but maybe there should be a separator since it's a different kind of action form Rename/Trash/Delete