patch 9.0.0753: some Ex commands are not in the help index

Problem:    Some Ex commands are not in the help index.
Solution:   Add the missing commands.  Add a script to check all Ex commands
            are in the help index. (Yee Cheng Chin, closes #11371)
diff --git a/src/version.c b/src/version.c
index bedbdc0..3bb2a2f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    753,
+/**/
     752,
 /**/
     751,