refactor: used loaded over mounted (#179)

packages/pinball_components/lib/src/components/layer.dart

@@ -21,8 +21,7 @@ mixin Layered<T extends Forge2DGame> on BodyComponent<T> {
   set layer(Layer value) {
     _layer = value;
     if (!isLoaded) {
-      // TODO(alestiago): Use loaded.whenComplete once provided.
-      mounted.whenComplete(_applyMaskBits);
+      loaded.whenComplete(_applyMaskBits);
     } else {
       _applyMaskBits();
     }

packages/pinball_components/test/src/components/layer_test.dart

@@ -57,8 +57,6 @@ void main() {
         const expectedLayer = Layer.spaceshipEntranceRamp;
         final component = TestLayeredBodyComponent()..layer = expectedLayer;
         await game.ensureAdd(component);
-        // TODO(alestiago): modify once component.loaded is available.
-        await component.mounted;
 
         _expectLayerOnFixtures(
           fixtures: component.body.fixtures,
@@ -79,8 +77,6 @@ void main() {
         component.layer = expectedLayer;
 
         await game.ensureAdd(component);
-        // TODO(alestiago): modify once component.loaded is available.
-        await component.mounted;
 
         _expectLayerOnFixtures(
           fixtures: component.body.fixtures,