patch 9.1.1138: cmdline completion for :hi is too simplistic

Problem:  Existing cmdline completion for :highlight was barebone and
          only completed the highlight group names.

Solution: Implement full completion for the highlight group arguments
          such as guifg and cterm. If the user tries to complete
          immediately after the '=' (e.g. `hi Normal guifg=<Tab>`), the
          completion will fill in the existing value, similar to how
          cmdline completion for options work (Yee Cheng Chin).

closes: #16712

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/cmdexpand.pro b/src/proto/cmdexpand.pro
index dfa6d1b..bfcc5c8 100644
--- a/src/proto/cmdexpand.pro
+++ b/src/proto/cmdexpand.pro
@@ -17,6 +17,7 @@
 void set_cmd_context(expand_T *xp, char_u *str, int len, int col, int use_ccline);
 int expand_cmdline(expand_T *xp, char_u *str, int col, int *matchcount, char_u ***matches);
 int ExpandGeneric(char_u *pat, expand_T *xp, regmatch_T *regmatch, char_u ***matches, int *numMatches, char_u *((*func)(expand_T *, int)), int escaped);
+int ExpandGenericExt(char_u *pat, expand_T *xp, regmatch_T *regmatch, char_u ***matches, int *numMatches, char_u *((*func)(expand_T *, int)), int escaped, int sortStartIdx);
 void globpath(char_u *path, char_u *file, garray_T *ga, int expand_options, int dirs);
 int wildmenu_translate_key(cmdline_info_T *cclp, int key, expand_T *xp, int did_wild_list);
 int wildmenu_process_key(cmdline_info_T *cclp, int key, expand_T *xp);