Backend cleanup (#2859)

* Extender docblocks cleanup
* Excplicit type hinting in extenders
* Bring method under constructor
* Mark some classes and methods as internal
* Remove beta references

Co-authored-by: Clark Winkelmann <clark.winkelmann@gmail.com>

src/Http/RouteCollection.php

@@ -13,6 +13,9 @@ use FastRoute\DataGenerator;
 use FastRoute\RouteParser;
 use Illuminate\Support\Arr;
 
+/**
+ * @internal
+ */
 class RouteCollection
 {
     /**

src/Http/RouteCollectionUrlGenerator.php

@@ -9,6 +9,9 @@
 
 namespace Flarum\Http;
 
+/**
+ * @internal
+ */
 class RouteCollectionUrlGenerator
 {
     /**

src/Http/RouteHandlerFactory.php

@@ -16,6 +16,9 @@ use InvalidArgumentException;
 use Psr\Http\Message\ServerRequestInterface as Request;
 use Psr\Http\Server\RequestHandlerInterface as Handler;
 
+/**
+ * @internal
+ */
 class RouteHandlerFactory
 {
     /**