vim counts (#2958)

Release Notes:

- vim: Fix counts with operators (`2yy`, `d3d`, etc.)
([#1496](https://github.com/zed-industries/community/issues/1496))
([#970](https://github.com/zed-industries/community/issues/970)).
- vim: Add support for counts with insert actions (`2i`, `2o`, `2a`,
etc.)
- vim: add `_` and `g_`