Problem: matchparen highlight not cleared in completion mode
Solution: Clear matchparen highlighting in completion mode
Remove hard-coded hack in insexpand.c to clear the :3match before
displaying the completion menu.
Add a test for matchparen highlighting. While at it, move all test tests
related to the matchparen plugin into a separate test file.
closes: vim/vim#13493closes: vim/vim#135249588666360
Co-authored-by: Christian Brabandt <cb@256bit.org>
