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/dumps/vim_ex_function_01.dump

@@ -17,4 +17,4 @@
 |e+0#af5f00255&|n|d|f|u|n|c|t|i|o|n| +0#0000000&@63
 @75
 |f+0#af5f00255&|u|n|c|t|i|o|n| +0#0000000&|{|"|F|"|}|o|{|"|o|"|}|(+0#e000e06&|)| +0#0000000&@52
-@57|1|9|,|1| @10|7|%| 
+@57|1|9|,|1| @10|6|%|