[10.x] Uses PHP Native Type Declarations 🐘 (#6010)

* Adds basic typing around method's arguments and return types

* Adds missing `closure` type

* Adds typing on tests

* Fixes `RedirectIfAuthenticated`

* Fixes `Authenticate`

* Improves `RedirectIfAuthenticated` types

* Fixes user factory `unverified` return type

tests/Unit/ExampleTest.php

@@ -8,10 +8,8 @@ class ExampleTest extends TestCase
 {
     /**
      * A basic test example.
-     *
-     * @return void
      */
-    public function test_that_true_is_true()
+    public function test_that_true_is_true(): void
     {
         $this->assertTrue(true);
     }