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_visual_block_mode.json

@@ -11,7 +11,7 @@
 {"Key":"$"}
 {"Get":{"state":"The «quick brownˇ»\nfox «jumps overˇ»\nthe «lazy dogˇ»","mode":"VisualBlock"}}
 {"Key":"shift-f"}
-{"Key":" "}
+{"Key":"space"}
 {"Get":{"state":"The «quickˇ» brown\nfox «jumpsˇ» over\nthe «lazy ˇ»dog","mode":"VisualBlock"}}
 {"Key":"v"}
 {"Get":{"state":"The «quick brown\nfox jumps over\nthe lazy ˇ»dog","mode":"Visual"}}