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_folds.json

@@ -17,6 +17,7 @@
 {"Key":"down"}
 {"Key":"y"}
 {"Key":"y"}
+{"Get":{"state":"fn boop() {\nˇ  barp()\n  bazp()\n}\n","mode":"Normal"}}
 {"ReadRegister":{"name":"\"","value":"  barp()\n  bazp()\n"}}
 {"Key":"z"}
 {"Key":"o"}