runtime(vim): Update base-syntax, improve :augroup highlighting (vim/vim#14125)
- Explicitly match the bang and group name in :aug! {name}.
- Allow any characters in a group name.
- Match default group switch marker, END.
- Match :aug without arguments (list command).
c4aef9a97b
Co-authored-by: dkearns <dougkearns@gmail.com>