[php-src] Issue #21190: get_declared_interfaces() does not include interfaces extending from other interfaces if script returns early

Issue: https://github.com/php/php-src/issues/21190
Author: tiberiusteng

### Description

The following code:

```php
<?php
print_r(get_declared_interfaces());
print_r(get_declared_classes());
if (interface_exists('a')) {
    return;
}

interface a {}
interface b extends a {}

class c {}
class d extends c {}
```

Only `a` appear in `get_declared_interfaces()`, both `c` and `d` appear in `get_declared_classes()`, perhaps they should be consistent?

We were trying to use `if (interface_exists('a')) exit;` to prevent redeclaring an interface (upgrading legacy code from require_once to SPL autoload), but discovered that adding `interface_exists()` to old code would prevent them being loaded even when there are no new autoloaded version registered.

Also at first we are assuming `get_declared_interfaces()`, `get_declared_classes()` won't include code after them, but seems this is expected behavior.

### PHP Version

```plain
PHP 8.5.2 (cli) (built: Jan 13 2026 21:40:53) (NTS)
Copyright (c) The PHP Group
Built by Homebrew
Zend Engine v4.5.2, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.2, Copyright (c), by Zend Technologies
```

### Operating System

_No response_