runtime(vim): Update base-syntax, fix :unabbrev highlighting (#14077)

Fixes issue #7876

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

runtime/syntax/testdir/input/vim_ex_abbreviate.vim

@@ -0,0 +1,25 @@
+" Vim :abbreviate commands
+
+abbrev <buffer> foo foobar
+cabbrev <buffer> cfoo cfoobar
+iabbrev <buffer> ifoo cfoobar
+
+abbrev <expr> <buffer> foo foobar
+cabbrev <expr> <buffer> cfoo cfoobar
+iabbrev <expr> <buffer> ifoo cfoobar
+
+noreabbrev <buffer> foo foobar
+cnoreabbrev <buffer> cfoo cfoobar
+inoreabbrev <buffer> ifoo cfoobar
+
+abbrev <expr> <buffer> foo foobar
+cabbrev <expr> <buffer> cfoo cfoobar
+iabbrev <expr> <buffer> ifoo cfoobar
+
+unabbrev <buffer> foo
+cunabbrev <buffer> cfoo
+iunabbrev <buffer> ifoo
+
+abclear <buffer>
+cabclear <buffer>
+iabclear <buffer>