Hides and disables all mutating editor actions for readonly editors.

Certain actions (as cmd-backspace mentioned in the issue) could be
somewhat beneficial to have for navigation purposes, but we'd better
shape that story properly, let's build a "harness" and disable the
mutating ones first.

Closes https://github.com/zed-industries/zed/issues/47333

Release Notes:

- Fixed readonly editor having certain mutation actions enabled