Symfony version(s) affected: 4.3.x-dev

Description
Since #30541 the inheritance hierarchy of \Symfony\Component\BrowserKit\Client has changed. Notably the test.client no longer is an instance of \Symfony\Component\BrowserKit\Client.

This breaks breaks at least https://github.com/FriendsOfBehat/SymfonyExtension and https://github.com/minkphp/MinkBrowserKitDriver and most probably other bundles using test.client.

How to reproduce

On Symfony 4.2 the following test case succeeds, on the master (4.3) branch this fails:

class TestClientTest extends \Symfony\Bundle\FrameworkBundle\Test\WebTestCase {
    public function testIsAClient()
    {
        $browser = static::createClient();
        $this->assertInstanceOf(\Symfony\Component\BrowserKit\Client::class, $browser);
    }
}

Possible Solution
Use a class_alias solution as described in #30541.