patch 8.2.2511: Vim9: cannot use Vim9 script syntax in some places

Problem:    Vim9: cannot use Vim9 script syntax in some places.
Solution:   Add the :vim9cmd command modifier. Incompatible: Makes ":vim9"
            mean ":vim9cmd" instead of ":vim9script".
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index 01c6156..e82e91b 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -1679,6 +1679,9 @@
 EXCMD(CMD_vimgrepadd,	"vimgrepadd",	ex_vimgrep,
 	EX_RANGE|EX_BANG|EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM|EX_TRLBAR|EX_XFILE|EX_LOCK_OK,
 	ADDR_OTHER),
+EXCMD(CMD_vim9cmd,	"vim9cmd",	ex_wrongmodifier,
+	EX_NEEDARG|EX_EXTRA|EX_NOTRLCOM|EX_CMDWIN|EX_LOCK_OK,
+	ADDR_NONE),
 EXCMD(CMD_vim9script,	"vim9script",	ex_vim9script,
 	EX_WORD1|EX_CMDWIN|EX_LOCK_OK,
 	ADDR_NONE),