[9.x] Add assertRedirectToRoute to TestResponse

[zaherg]

Illuminate\Testing\TestResponse has several helpers to assert the response has a redirect of various types. There is assertRedirect(string $uri = null), assertRedirectContains(string $uri), and assertRedirectToSignedRoute(string $name = null, array $parameters = []).

This PR add a missing assertion assertRedirectToRoute, which in theory does not differ much from assertRedirectToSignedRoute.

Used as the following:

$this->get('test-route')
    ->assertRedirectToRoute('named-route');

and in case of passing parameters we use it as the following:

$this->get('test-route')
    ->assertRedirectToRoute('named-route-with-param', 'hello');

$this->get('test-route-with-extra-param')
    ->assertRedirectToRoute('named-route-with-param', [
        'param' => 'foo',
        'extra' => 'another',
    ]);

[gms8994]

The assertRedirectToRoute function suggests that it can take a null value, but passing in a null value throws an error:

See this test case for PoC:

public function testAssertRedirectToRouteWithoutRouteName()
{
    $this->router->get('test-route', function () {
        return new RedirectResponse($this->urlGenerator->route('named-route'));
    });

    $this->get('test-route')
        ->assertRedirectToRoute();
}

[zaherg]

I'll push new code in a few min.

thanks @gms8994 for catching this, I added your test to the code to make sure everything is working as it should.