codemirror file view: Add search widget

Created by: fkling

This adds CodeMirror's default search functionality. This works now because the file view is focusable. When focused (e.g. by clicking into it), meta+f will show CodeMirror's search input.

This currently uses it's own default style but we might be able to either customize it via CSS or we can completely render our own UI (the search extension allows to do that).

Test plan

Enable CodeMirror file view, focus it, press meta+f to search.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.