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/input/vim_ex_highlight.vim

@@ -0,0 +1,55 @@
+" Vim :highlight command
+
+" list
+highlight
+highlight Comment
+
+" reset
+highlight clear
+
+" disable
+highlight clear Comment
+highlight Comment NONE
+
+" add/modify
+highlight Comment cterm=underline
+highlight default Comment term=bold
+
+" link
+highlight link Foo Comment
+highlight! link Foo Comment
+highlight link Foo NONE
+highlight! link Foo NONE
+
+" default link
+highlight default link Foo Comment
+highlight! default link Foo Comment
+highlight default link Foo NONE
+highlight! default link Foo NONE
+
+
+" line continuation and command separator
+
+hi Comment
+      "\ comment
+      \ term=bold
+      "\ comment
+      \ ctermfg=Cyan
+      \ guifg=#80a0ff
+      \ gui=bold
+
+hi Comment
+      \ term=bold
+      \ ctermfg=Cyan
+      \ guifg=#80a0ff
+      \ gui=bold | echo "Foo"
+
+hi Comment term=bold ctermfg=Cyan guifg=#80a0ff gui=bold | echo "Foo"
+
+hi default link
+      \ Foo
+      \ Comment
+
+hi default link
+      \ Foo
+      \ Comment | echo "Foo"