patch 9.1.0476: Cannot see matched text in popup menu

Problem:  Cannot see matched text in popup menu
Solution: Introduce 2 new highlighting groups: PmenuMatch and
          PmenuMatchSel (glepnir)

ping @habamax, @neutaaaaan @romainl because vim/colorschemes may need
some updates, @lifepillar for updating vim-colortemplate

closes: #14694

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

src/insexpand.c

@@ -1431,6 +1431,15 @@ ins_compl_show_pum(void)
 #define DICT_FIRST	(1)	// use just first element in "dict"
 #define DICT_EXACT	(2)	// "dict" is the exact name of a file
 
+/*
+ * Get current completion leader
+ */
+    char_u *
+ins_compl_leader(void)
+{
+    return compl_leader;
+}
+
 /*
  * Add any identifiers that match the given pattern "pat" in the list of
  * dictionary files "dict_start" to the list of completions.