runtime(vim): Update base-syntax, improve :echo and :execute highlighting (#14199)

Improve :echo and :execute highlighting.

- Add better line-continuation support for both commands.
- Improve the :execute command's expression argument matching.
- Remove the fix for issue #9987 as this is now handled by correctly
  matching the parens in :echo (...) as operator parens.


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

runtime/syntax/testdir/input/vim_ex_echo.vim

@@ -15,6 +15,24 @@ echo "Answer = "
      "\ comment
       \ 42
 
+echo
+      \ "Answer = "
+     "\ comment
+      \ 42
+
 " :echo without {expr}
 echo| echo "Foo"
 
+" trailing comment needs |
+echo "foo" | " comment
+
+
+" Issue #9987 (parenthesised argument - not a function call)
+
+let foo = {'end': 123}
+
+if 123
+	echo (foo.end)
+else
+	echo 'bar'
+endif