patch 9.1.0936: cannot highlight completed text

Problem:  cannot highlight completed text
Solution: (optionally) highlight auto-completed text using the
          ComplMatchIns highlight group (glepnir)

closes: #16173

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/highlight.c

@@ -262,6 +262,7 @@ static char *(highlight_init_both[]) = {
     "default link PmenuMatchSel PmenuSel",
     "default link PmenuExtra Pmenu",
     "default link PmenuExtraSel PmenuSel",
+    "default link ComplMatchIns Normal",
     CENT("Normal cterm=NONE", "Normal gui=NONE"),
     NULL
 };