vim: keymap tweaks (#2674)

A few small tweaks to fix some of the community issues

Release Notes:

- vim: Fix `escape` in command palette
([#1347](https://github.com/zed-industries/community/issues/1347)).
- vim: Allow `^` as a motion in actions
([#856](https://github.com/zed-industries/community/issues/856)).
- vim: Allow `ctrl-c` to exit visual mode
([#1447](https://github.com/zed-industries/community/issues/1447)).