[12.x] Infinite method chaining in contextual binding builder

[daniser]

This PR enables infinite chaining of ContextualBindingBuilder methods.

Before:

$this->app->when(MyService::class)->needs(Repository::class)->give(
    fn () => Cache::store(config('my-service.cache.store'))
);
$this->app->when(MyService::class)->needs('$ttl')->giveConfig('my-service.cache.ttl');

After:

$this->app->when(MyService::class)
    ->needs(Repository::class)->give(
        fn () => Cache::store(config('my-service.cache.store'))
    )
    ->needs('$ttl')->giveConfig('my-service.cache.ttl');