patch 8.2.2598: Vim9: :open does not need to be supported

Problem:    Vim9: :open does not need to be supported.
Solution:   Do not support :open in Vim9 script.

src/ex_docmd.c

@@ -6609,6 +6609,10 @@ ex_open(exarg_T *eap)
     regmatch_T	regmatch;
     char_u	*p;
 
+#ifdef FEAT_EVAL
+    if (not_in_vim9(eap) == FAIL)
+	return;
+#endif
     curwin->w_cursor.lnum = eap->line2;
     beginline(BL_SOL | BL_FIX);
     if (*eap->arg == '/')

src/testdir/test_vim9_script.vim

@@ -1880,6 +1880,8 @@ def Test_no_insert_xit()
   CheckScriptFailure(['vim9script', 'c'], 'E1100:')
   CheckScriptFailure(['vim9script', 'i = 1'], 'E488:')
   CheckScriptFailure(['vim9script', 'i'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'o = 1'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'o'], 'E1100:')
   CheckScriptFailure(['vim9script', 't'], 'E1100:')
   CheckScriptFailure(['vim9script', 't = 1'], 'E1100:')
   CheckScriptFailure(['vim9script', 'x = 1'], 'E1100:')

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2598,
 /**/
     2597,
 /**/

src/vim9script.c

@@ -102,6 +102,7 @@ not_in_vim9(exarg_T *eap)
 	    case CMD_append:
 	    case CMD_change:
 	    case CMD_insert:
+	    case CMD_open:
 	    case CMD_t:
 	    case CMD_xit:
 		semsg(_(e_command_not_supported_in_vim9_script_missing_var_str), eap->cmd);