runtime(vim): Update base-syntax and generator, only match valid predefined variables

- Only match valid predefined and option variables.
- Match scope dictionaries.
- Highlight scope prefixed variables as a scope dictionary accessor. The
  vimVarScope syntax group can be linked to vimVar to disable this.
- Include support for Neovim-only predefined and option variables.

Temporary collateral damage - scope dictionaries match instead of keys
in dictionary literals.

closes: #16727

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

runtime/syntax/testdir/input/vim_ex_function.vim

@@ -163,6 +163,20 @@ function Foo(
   return 42
 endfunction
 
+
+" arguments
+
+function Foo(a, b, c)
+  echo a:a a:b a:c
+endfunction
+
+function Foo(...)
+  echo a:000
+  echo a:0
+  echo a:1 a:2 a:3 a:4 a:5 a:6 a:7 a:8 a:9 a:10 a:11 a:12 a:13 a:14 a:15 a:16 a:17 a:18 a:19 a:20
+endfunction
+
+
 " Issue #16243 (vimscript def parameters syntax highlight is wrong)
 
 function Test(lines = [line('.'), line('.')])