Closes#13579
A major painpoint in the Vim crate has been life-cycle management. We
used to have one global Vim instance that tried to track per-editor
state; this led to a number of subtle issues (e.g. #13579, the mode
indicator being global, and quick toggling between windows letting vim
mode's notion of the active editor get out of sync).
This PR changes the internal structure of the code so that there is now
one `Vim` instance per `Editor` (stored as an `Addon`); and the global
stuff is separated out. This fixes the above problems, and tidies up a
bunch of the mess in the codebase.
Release Notes:
* vim: Fixed accidental visual mode in project search and go to
references
([#13579](https://github.com/zed-industries/zed/issues/13579)).
