runtime(vim): Update base-syntax, improve function definition matching

- Fix highlighting of function names including /fu\%[nction]/ (E.g.,
  s:func(), foo.fu(), fu.func())
- Match :delfunction argument.

Reported by Aliaksei Budavei.

closes: #17428

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

runtime/syntax/testdir/input/vim_ex_delfunction.vim

@@ -0,0 +1,34 @@
+" Vim :delfunction command
+
+
+delfunction Foo
+delfunction <SID>Foo
+delfunction foo.bar
+delfunction g:foo.bar
+delfunction s:foo.bar
+delfunction foo#bar
+delfunction g:foo#bar
+delfunction foo#bar.baz
+delfunction g:foo#bar.baz
+
+
+delfunction! Foo
+delfunction! <SID>Foo
+delfunction! foo.bar
+delfunction! g:foo.bar
+delfunction! s:foo.bar
+delfunction! foo#bar
+delfunction! g:foo#bar
+delfunction! foo#bar.baz
+delfunction! g:foo#bar.baz
+
+
+delfunction Foo | echo "Foo"
+delfunction Foo " comment
+
+
+" Issue https://github.com/vim/vim/pull/17420#issuecomment-2927798687
+" (arg named /fu%\[nction]/)
+
+silent! delfunc! func
+