[5.x] Add support for $view parameter closure with Statamic::route()

[jesseleite]

This PR adds support for optional $view parameter closure with Statamic::route(), so that you can dynamically render a view from a route segment.

For example, this works fine in Laravel...

Route::get('/components/{component}', function ($component) {
    return view($component);
});

So this should work with Statamic routes as well...

Route::statamic('/components/{component}', function ($component) {
    return view($component);
});

References #9953