runtime(vim): Update base-syntax, improve function definition highlighting (#14203)

Improve function definition highlighting.

- Match bang and function modifiers - abort etc.
- Only match valid scope modifiers.
- Match listing commands.
- Don't match ex commands in function names.
- Split function syntax groups into :func and :def subgroups.
- Match Vim9-script parameter and return types.
- Limit legacy-script and Vim9-script comments to :func and :def
  definitions, respectively.

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/generator/gen_syntax_vim.vim

@@ -279,6 +279,7 @@ function! s:get_vim_command_type(cmd_name)
 	\	'autocmd', 'augroup', 'doautocmd', 'doautoall',
 	\	'echo', 'echoconsole', 'echoerr', 'echohl', 'echomsg', 'echon', 'echowindow',
 	\	'execute',
+	\ 'function', 'endfunction', 'def', 'enddef',
 	\	'behave', 'augroup', 'normal', 'syntax',
 	\	'append', 'insert',
 	\	'Next', 'Print', 'X',