feat: FlameIsolate - a neat way of handling threads (#1909)

Adding a bridge library for integral_isolates adding support for components to run CPU intensive code with a function similar to Flutter's compute function, but with a long lived isolate. Lifecycle is handled by the game loop, where the isolate would live between onMount and onRemove.

packages/flame_isolate/example/lib/terrain/grass.dart

@@ -0,0 +1,24 @@
+import 'package:flame/components.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_isolates_example/terrain/terrain.dart';
+
+class Grass extends PositionComponent with Terrain {
+  static final _color = Paint()..color = const Color(0xff567d46);
+  static final _debugColor = Paint()..color = Colors.black.withOpacity(.5);
+
+  late final _rect = size.toRect();
+  late final _rect2 = Rect.fromCenter(
+    center: _rect.center,
+    height: 10,
+    width: 10,
+  );
+
+  @override
+  void render(Canvas canvas) {
+    canvas.drawRect(_rect, _color);
+    canvas.drawRect(_rect2, _debugColor);
+  }
+
+  @override
+  double difficulty = 1.0;
+}