runtime(vim): Update base-syntax, improve :echo and :execute highlighting (vim/vim#14199)
Improve :echo and :execute highlighting.
- Add better line-continuation support for both commands.
- Improve the :execute command's expression argument matching.
- Remove the fix for issue vim/vim#9987 as this is now handled by correctly
matching the parens in :echo (...) as operator parens.
61887b3d6f
Co-authored-by: dkearns <dougkearns@gmail.com>