Allow DateTimeImmutable in datefmt_format_object()

As pointed out in a comment on bug #65683.

Author: nikic

ext/intl/dateformat/dateformat_format_object.cpp

@@ -169,7 +169,7 @@ U_CFUNC PHP_FUNCTION(datefmt_format_object)
 			goto cleanup;
 		}
 		cal = obj_cal->clone();
-	} else if (instanceof_function(instance_ce, php_date_get_date_ce())) {
+	} else if (instanceof_function(instance_ce, php_date_get_interface_ce())) {
 		if (intl_datetime_decompose(object, &date, &timeZone, NULL,
 				"datefmt_format_object") == FAILURE) {
 			RETURN_FALSE;

ext/intl/tests/dateformat_bug65683_2.phpt

@@ -0,0 +1,12 @@
+--TEST--
+Bug #65683: Intl does not support DateTimeImmutable (using datefmt_format_object)
+--FILE--
+<?php
+$date = date_create('1970-01-01');
+$date_imm = date_create_immutable('1970-01-01');
+var_dump(datefmt_format_object($date, null, 'fr_FR'));
+var_dump(datefmt_format_object($date_imm, null, 'fr_FR'));
+?>
+--EXPECT--
+string(24) "1 janv. 1970 à 00:00:00"
+string(24) "1 janv. 1970 à 00:00:00"