patch 8.2.3712: cannot use Vim9 lambda for 'tagfunc'

Problem:    Cannot use Vim9 lambda for 'tagfunc'.
Solution:   Make it work, add more tests. (Yegappan Lakshmanan, closes #9250)
diff --git a/src/insexpand.c b/src/insexpand.c
index e9b4861..630548b 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2257,13 +2257,12 @@
 }
 
 /*
- * Execute user defined complete function 'completefunc' or 'omnifunc', and
- * get matches in "matches".
+ * Execute user defined complete function 'completefunc', 'omnifunc' or
+ * 'thesaurusfunc', and get matches in "matches".
+ * "type" is either CTRL_X_OMNI or CTRL_X_FUNCTION or CTRL_X_THESAURUS.
  */
     static void
-expand_by_function(
-    int		type,	    // CTRL_X_OMNI or CTRL_X_FUNCTION
-    char_u	*base)
+expand_by_function(int type, char_u *base)
 {
     list_T      *matchlist = NULL;
     dict_T	*matchdict = NULL;