runtime(vim): Improve Vim9 and legacy-script comment highlighting (vim/vim#13104)
This is a first-pass attempt to limit matching of Vim9 and legacy-script
comments to the appropriate syntactic contexts.
Vim9-script comments are highlighted at top level in a Vim9-script file,
in all :def functions, and in all :autocmd and :commmand command blocks.
Legacy-script comments are highlighted at top level in a legacy script
file, in all :func functions and in the Vim9-script preamble before the
:vim9script marker command.
Fixesvim/vim#13047, vim/vim#11307 and vim/vim#9587.
04e5363b82
Co-authored-by: dkearns <dougkearns@gmail.com>
d627497156
