patch 8.2.2728: special key names don't work if 'isident' is cleared

Problem:    Special key names don't work if 'isident' is cleared.
Solution:   Add vim_isNormalIDc() and use it for special key names.
            (closes #2389)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2728,
 /**/
     2727,
 /**/