vim-patch:6ac2e4a: runtime(vim): Update base syntax, improve function call highlighting (#34874)

- Match more function calls.
- Contain function call syntax groups.
- Improve differentiation between Ex commands and builtin functions with
  the same name.  Remove special cases.  Command modifiers are not
  currently well differentiated from functions.

closes: vim/vim#17712

6ac2e4aa0a

Co-authored-by: Doug Kearns <dougkearns@gmail.com>

test/functional/vimscript/api_functions_spec.lua

@@ -202,7 +202,7 @@ describe('eval-API', function()
     screen:expect([[
       {15:call} {25:bufnr}{16:(}{26:'%'}{16:)}                         |
       {15:call} {25:nvim_input}{16:(}{26:'typing...'}{16:)}            |
-      {15:call} not_a_function{16:(}{26:42}{16:^)}                 |
+      {15:call} {9:not_a_function}{16:(}{26:42}{16:^)}                 |
       {1:~                                       }|*4
                                               |
     ]])