[php-src] Issue #20925: restore_exception_handler does not work as expected

Issue: https://github.com/php/php-src/issues/20925
Author: Appla

### Description

After commit https://github.com/php/php-src/commit/3301d9602a2307007858c299c41795d3d95e3843,  the behavior of  `zend_user_exception_handler` has  changed. As a result, call `set_exception_handler` / `restore_exception_handler` inside exception handler no longer behaves as expected

Is this the intended behavior, or a regression?

The following code:

```php
<?php
register_shutdown_function(function() {
    echo "DEBUG: Shutdown function 1\n";
});

register_shutdown_function(function() {
    echo "DEBUG: Shutdown function 2 will throw\n";
    throw new \RuntimeException("throw in shutdown_func");
});

set_exception_handler(function($e) {
    $rc['restore_error_handler'] = \restore_error_handler();
    $rc['restore_exception_handler'] = \restore_exception_handler();
    // $rc['restore_exception_handler_2'] = \restore_exception_handler();
    echo sprintf("DEBUG: got exception[code: %d, error: %s]", $e->getCode(), $e->getMessage()), json_encode($rc), PHP_EOL;
});

echo PHP_VERSION, PHP_EOL;
throw new RuntimeException('first exception');
```

Resulted in this output:
```
8.4.16
DEBUG: got exception[code: 0, error: first exception]{"restore_error_handler":true,"restore_exception_handler":true}
DEBUG: Shutdown function 1
DEBUG: Shutdown function 2 will throw
DEBUG: got exception[code: 0, error: throw in shutdown_func]{"restore_error_handler":true,"restore_exception_handler":true}
```

But I expected this output instead:
```
7.4.33
DEBUG: got exception[code: 0, error: first exception]{"restore_error_handler":true,"restore_exception_handler":true}
DEBUG: Shutdown function 1
DEBUG: Shutdown function 2 will throw
PHP Fatal error:  Uncaught RuntimeException: throw in shutdown_func in /root/t.p:9
Stack trace:
#0 [internal function]: {closure}()
#1 {main}
  thrown in /path/to/test.php on line 9
```


### PHP Version

```plain
PHP 8.4.16 (cli) (built: Dec 16 2025 16:03:34) (NTS gcc x86_64)
Copyright (c) The PHP Group
Built by Remi's RPM repository <https://rpms.remirepo.net/> #StandWithUkraine
Zend Engine v4.4.16, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.16, Copyright (c), by Zend Technologies

PHP 7.4.33 (cli) (built: Dec 18 2025 08:02:40) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.33, Copyright (c), by Zend Technologies
```

### Operating System

Fedora 42