vim test redux (#11709)

This cleans up the neovim-backed vim tests:
- removed exempted tests (we'll rely on bug reports to find missing edge
cases)
- moved all assertions into non-async fn's so that failures are
reporting on the right file/line
- removed the NeovimBackedBindingTestContext
- renamed a few things to make them clearer
- reduced the number of permutations tested in some cases to reduce
slowest test from 60s to 5s

Release Notes:

- N/A

crates/vim/test_data/test_change_cc.json

@@ -6,7 +6,7 @@
 {"Key":"c"}
 {"Key":"c"}
 {"Get":{"state":"ˇ\nbrown fox\njumps over\nthe lazy","mode":"Insert"}}
-{"Put":{"state":"The quick\n  broˇwn fox\njumˇps over\nthe lazy"}}
+{"Put":{"state":"The quick\n  broˇwn fox\njumps over\nthe lazy"}}
 {"Key":"c"}
 {"Key":"c"}
-{"Get":{"state":"The quick\n  ˇ\nˇ\nthe lazy","mode":"Insert"}}
+{"Get":{"state":"The quick\n  ˇ\njumps over\nthe lazy","mode":"Insert"}}