[8.x] Don't name unnamed routes inside a group with a prefix

[tobyzerner]

Currently if you register an unnamed route within a group with a name prefix, the route's name is set to the prefix.

$router->name('api.')->group(function ($router) {
    $router->get('users', 'UsersController@index');
});

$routes = $router->getRoutes()->get();
echo last($routes)->getName(); // "api."

While the consequences of this are somewhat obscure (but definitely exist), it is indeed odd behavior and I would expect getName() to return null in the above example since I never explicitly set a name on the route.

This PR attempts to fix that within the constraints of the current architecture. I'm not sure if this would be considered a breaking change vs a bug fix, but I can PR this instead to master if desired.

Basically, instead of passing the group's $action['as'] value into each new route created within it, it passes it as $action['as_prefix']. Then when a name is set on a route, it prepends $action['as_prefix'].

This also changes the behavior of calling name more than once on a route. Previously each time you called it, the value passed would be continually appended:

$router->name('api.')->group(function ($router) {
    $router->get('users', 'UsersController@index')->name('foo')->name('bar') // "api.foobar"
});

Now, the value will be appended onto the initial group prefix each time:

$router->name('api.')->group(function ($router) {
    $router->get('users', 'UsersController@index')->name('foo')->name('bar') // "api.bar"
});

[devcircus]

Seems like a common sense change but worried it would be a breaking change for a lot of apps. I've see a number of apps with route "groups" for individual routes and using the group name for the route. I know I've ended up with one route in a group after moving other routes out of the group and never refactoring. IMO this should go into the next version with a note in the upgrade guide.

[driesvints]

This is a huge breaking change.

[tobyzerner]

@taylorotwell would you accept this for master/9.x? Or not interested?