[php-src] Issue #9556: "iterable" alias "array|Traversable" breaks PHP 8.1 code

Issue: https://github.com/php/php-src/issues/9556 Author: cziegenberg ### Description I just recognized a problem in a project when testing it with PHP 8.2RC2 (API Platform 3.0). There is an interface that contains a method with the return type definition "object|iterable|null". In PHP 8.2 "iterable" becomes "array|Traversable" and so the return type definition results in "object|array|Traversable|null", which now contains the redundant "Traversable" type (although "object" is already contained) and leads to a fatal error. Eample... The following code: ```php <?php class Foo { public function bar(): object|iterable|null { return null; } } echo 'baz'; ``` Resulted in this output: ``` Fatal error: Type Traversable|object|array|null contains both object and a class type, which is redundant in [... ``` But I expected this output instead: ``` baz ``` As a workaround one could use "object|array" instead of "object|iterable", but best would be if the change in PHP 8.2 handles this special case, to avoid this break... Otherwise this should be listed in "Backward Incompatible Changes" instead of "Other Changes". ### PHP Version PHP 8.2.0RC2 ### Operating System _No response_