runtime(vim): Update base-syntax file, improve class, enum and interface highlighting

- Enable folding of class, enum and interface declarations.
- Highlight constructor names with the Function highlight group, like
  other special methods.
- Mark function definitions using special method names as errors.
- Highlight :type arguments.

fixes: #14393#issuecomment-2042796198.
closes: #13810

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

runtime/syntax/testdir/input/vim_ex_menu.vim

@@ -76,7 +76,7 @@ popup! &Foo | echo "Foo"
 
 " a menu item name cannot start with '.'
 
-export def HistoryJumpMenu()
+def HistoryJumpMenu()
     popup.FilterMenu("Jump history", dir_hist,
         (res, _) => {
             HistoryJump(res.text)