feat: implemented basic SlingShot

lib/game/components/sling_shot.dart

@@ -1,9 +1,56 @@
 import 'package:flame_forge2d/flame_forge2d.dart';
+import 'package:flutter/material.dart';
+import 'package:pinball/game/game.dart';
 
+/// {@template sling_shot}
+/// Triangular [BodyType.static] body that propels the [Ball] toward the
+/// opposite side.
+///
+/// [SlingShot]s are usually positioned above each [Flipper].
+/// {@endtemplate sling_shot}
 class SlingShot extends BodyComponent {
+  /// @{macro sling_shot}
+  SlingShot({
+    required Vector2 position,
+  }) : _position = position {
+    // TODO(alestiago): Use sprite instead of color when provided.
+    paint = Paint()
+      ..color = const Color(0xFF00FF00)
+      ..style = PaintingStyle.fill;
+  }
+
+  /// The initial position of the [SlingShot] body.
+  final Vector2 _position;
+
+  List<FixtureDef> _createFixtureDefs() {
+    final fixtures = <FixtureDef>[];
+
+    final triangleVertices = [
+      Vector2(0, 0),
+      Vector2(0, -10),
+      Vector2(10, -10),
+    ];
+    final triangle = PolygonShape()..set(triangleVertices);
+    fixtures.add(FixtureDef(triangle));
+
+    final kickerVertices = [
+      triangleVertices.first,
+      triangleVertices.last,
+    ];
+    final kicker = PolygonShape()..set(kickerVertices);
+    final kickerFixtureDef = FixtureDef(kicker)..restitution = 2.0;
+    fixtures.add(kickerFixtureDef);
+
+    return fixtures;
+  }
+
   @override
   Body createBody() {
-    // TODO: implement createBody
-    throw UnimplementedError();
+    final bodyDef = BodyDef()..position = _position;
+
+    final body = world.createBody(bodyDef);
+    _createFixtureDefs().forEach(body.createFixture);
+
+    return body;
   }
 }