[php-src] Issue #9221: Defer loading `use` classes into memory (helps support ::class, infrequently used code paths, etc)

Issue: https://github.com/php/php-src/issues/9221 Author: garygreen ### Description Currently when adding a use class to a PHP file it will cause that class to be imported into memory, even if it's not actually subsequently used in the class. For example: ```php <?php use App\Support; ``` Lots of developers may do this in order to just use Support::class shortcut without realising the use statement loads all those classes into memory. Is there a way for PHP to know that file wasn't *actually* used, so doesn't need to load it into memory? If that's not easily possible, maybe this could be hinted through an attribute? ```php #[\DeferUse] use App\Support; ``` I would hope PHP can just defer loading the class into memory straight away for all use though, until it's actually needed. That would have a huge impact on all PHP apps reducing memory usage.