patch 8.2.3536: the do_highlight() function is way too long

Problem:    The do_highlight() function is way too long.
Solution:   Split it into several functions. (Yegappan Lakshmanan,
            closes #9011)
diff --git a/src/version.c b/src/version.c
index 555bd8e..2049889 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3536,
+/**/
     3535,
 /**/
     3534,