This isn't quite an exact emulation, as instead of using one selection
that is magically in "column mode", we emulate it with a bunch of zed
multi-selections (one per line).
I think this is better, as it requires fewer changes to the codebase,
and lets you see the impact of any changes immediately on all lines.
Fixes: zed-industries/community#984
These primarily happen when first entering visual mode, but can also
be created with objects like `vi{`.
Along the way fix the way ranges like `vi{` are selected to be more
similar to nvim.
As part of this I added `assert_shared_state()` to the
NeovimBackedTestContext so that it is more like a drop-in replacement
for the VimTestContext.
The remaining part of zed-industries/community#682 is adding bracket
matching to plain text. It looks like the current logic requires there
to be a tree sitter language for the language in order to support
bracket matching. I didn't fix this in this PR because I was unsure
whether to try and work around that, or to try and add a plain text tree
sitter language.
Release Notes:
- vim: support `{` and `}` for paragraph motion
([#470](https://github.com/zed-industries/community/issues/470)).
- vim: fix `%` at the end of the line
([#682](https://github.com/zed-industries/community/issues/682)).
