patch 8.2.3503: Vim9: using g:pat:cmd is confusing

Problem:    Vim9: using g:pat:cmd is confusing.
Solution:   Do not recognize g: as the :global command.  Also for s:pat:repl.
            (closes #8982)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 5c92e09..78a87e7 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3724,6 +3724,9 @@
 				// don't accept alphanumeric for separator
 	if (check_regexp_delim(*cmd) == FAIL)
 	    return;
+	if (in_vim9script() && check_global_and_subst(eap->cmd, eap->arg)
+								      == FAIL)
+	    return;
 
 	/*
 	 * undocumented vi feature:
@@ -4899,6 +4902,9 @@
     cmd = eap->arg;
     which_pat = RE_LAST;	    // default: use last used regexp
 
+    if (in_vim9script() && check_global_and_subst(eap->cmd, eap->arg) == FAIL)
+	return;
+
     /*
      * undocumented vi feature:
      *	"\/" and "\?": use previous search pattern.