When a key binding is deleted we keep the exact same scroll bar
position. When a keybinding is modified we select that keybinding in
it's new position and scroll to it.

I also changed save/modified keybinding to use fs.write istead of
fs.atomic_write. Atomic write was creating two FS events that some
scrollbar bugs when refreshing the keymap editor.

Co-authored-by: Ben \<ben@zed.dev\>

Release Notes:

- N/A