editor: Add ToggleTabBar action (#12499)

This PR adds the `editor: toggle tab bar` action that hides / shows the
tab bar and updates the `tab_bar.show` setting in `settings.json`
accordingly.

First mentioned in
https://github.com/zed-industries/zed/pull/7356#issuecomment-2118445379.

Release Notes:

- Added the `editor: toggle tab bar` action.