Migrate flame_forge2d to monorepo (#852)

* Migrate flame_forge2d to monorepo

* Put in the temporary publish to none

* Update docs

* Add dart_code_metrics

* Add analysis options

* Fix analyze issues

* Fix formatting

* Add dart_code_metrics to flame_forge2d example

packages/flame_forge2d/example/lib/draggable_sample.dart

@@ -0,0 +1,49 @@
+import 'package:flame_forge2d/flame_forge2d.dart';
+import 'package:flutter/material.dart' hide Draggable;
+import 'package:forge2d/forge2d.dart';
+import 'package:flame_forge2d/forge2d_game.dart';
+import 'package:flame/components.dart';
+import 'package:flame/extensions.dart';
+import 'package:flame/gestures.dart';
+
+import 'balls.dart';
+import 'boundaries.dart';
+
+class DraggableSample extends Forge2DGame with HasDraggableComponents {
+  DraggableSample() : super(gravity: Vector2.all(0.0));
+
+  @override
+  Future<void> onLoad() async {
+    await super.onLoad();
+    final boundaries = createBoundaries(this);
+    boundaries.forEach(add);
+    final center = screenToWorld(viewport.effectiveSize / 2);
+    add(DraggableBall(center));
+  }
+}
+
+class DraggableBall extends Ball with Draggable {
+  DraggableBall(Vector2 position) : super(position, radius: 5) {
+    originalPaint = Paint()..color = Colors.amber;
+    paint = originalPaint;
+  }
+
+  @override
+  bool onDragStart(int pointerId, DragStartInfo details) {
+    paint = randomPaint();
+    return true;
+  }
+
+  @override
+  bool onDragUpdate(int pointerId, DragUpdateInfo details) {
+    final worldDelta = Vector2(1, -1)..multiply(details.delta.game);
+    body.applyLinearImpulse(worldDelta * 1000);
+    return true;
+  }
+
+  @override
+  bool onDragEnd(int pointerId, DragEndInfo details) {
+    paint = originalPaint;
+    return true;
+  }
+}