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>
