runtime(vim): Update base-syntax, improve :highlight command (#14228)

Improve :highlight command highlighting

- Use the same highlight groups for "default link" with and without
  bang.
- Match some common line-continuation use.
- Match :hi clear variants.
- Highlight color-name values.

Resync vim.vim and generator/vim.vim.base.

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

runtime/syntax/testdir/dumps/vim_ex_highlight_00.dump

@@ -0,0 +1,20 @@
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