refactor: resolved gravityScale problems

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

@@ -79,7 +79,7 @@ class Ball<T extends Forge2DGame> extends BodyComponent<T>
   // TODO(allisonryan0002): prevent motion from contact with other balls.
   void stop() {
     body
-      ..gravityScale = 0
+      ..gravityScale = Vector2.zero()
       ..linearVelocity = Vector2.zero()
       ..angularVelocity = 0;
   }
@@ -88,7 +88,7 @@ class Ball<T extends Forge2DGame> extends BodyComponent<T>
   ///
   /// If previously [stop]ped, the previous ball's velocity is not kept.
   void resume() {
-    body.gravityScale = 1;
+    body.gravityScale = Vector2(0, 1);
   }
 
   @override

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

@@ -94,7 +94,7 @@ class ChromeDino extends BodyComponent with InitialPosition {
   @override
   Body createBody() {
     final bodyDef = BodyDef()
-      ..gravityScale = 0
+      ..gravityScale = Vector2.zero()
       ..position = initialPosition
       ..type = BodyType.dynamic;
 

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

@@ -120,7 +120,7 @@ class Flipper extends BodyComponent with KeyboardHandler, InitialPosition {
   Body createBody() {
     final bodyDef = BodyDef()
       ..position = initialPosition
-      ..gravityScale = 0
+      ..gravityScale = Vector2.zero()
       ..type = BodyType.dynamic;
     final body = world.createBody(bodyDef);
     _createFixtureDefs().forEach(body.createFixture);

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

@@ -35,7 +35,7 @@ class Plunger extends BodyComponent with InitialPosition {
       ..position = initialPosition
       ..userData = this
       ..type = BodyType.dynamic
-      ..gravityScale = 0;
+      ..gravityScale = Vector2.zero();
 
     return world.createBody(bodyDef)..createFixture(fixtureDef);
   }

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

@@ -48,7 +48,7 @@ void main() {
           final ball = Ball(baseColor: Colors.blue);
           await game.ensureAdd(ball);
 
-          ball.body.gravityScale = 0;
+          ball.body.gravityScale = Vector2.zero();
           ball.body.linearVelocity.setValues(10, 10);
           game.update(1);
           expect(ball.body.position, isNot(equals(ball.initialPosition)));
@@ -153,7 +153,7 @@ void main() {
             ball.stop();
             ball.resume();
 
-            ball.body.gravityScale = 0;
+            ball.body.gravityScale = Vector2.zero();
             ball.body.linearVelocity.setValues(10, 10);
             game.update(1);
             expect(ball.body.position, isNot(equals(ball.initialPosition)));