fix(flame): Export FixedResolutionViewport and make `withFixedResol…

…ution` a redirect constructor (#2817)

The CameraComponent.withFixedResolution was a factory but can easily be a redirect constructor, allowing developers to use it when they extend the CameraComponent. On top of that the FixedResolutionViewport was not being exported so if a developer wanted to have a custom camera with a FixedResolutionViewport there was no way to do so unless they imported from src/ or copied the code, both are bad practices 😄

packages/flame/lib/camera.dart

@@ -7,6 +7,8 @@ export 'src/camera/viewport.dart' show Viewport;
 export 'src/camera/viewports/circular_viewport.dart' show CircularViewport;
 export 'src/camera/viewports/fixed_aspect_ratio_viewport.dart'
     show FixedAspectRatioViewport;
+export 'src/camera/viewports/fixed_resolution_viewport.dart'
+    show FixedResolutionViewport;
 export 'src/camera/viewports/fixed_size_viewport.dart' show FixedSizeViewport;
 export 'src/camera/viewports/max_viewport.dart' show MaxViewport;
 export 'src/camera/world.dart' show World;

packages/flame/lib/src/camera/camera_component.dart

@@ -65,22 +65,20 @@ class CameraComponent extends Component {
   /// [height] pixels are visible within the viewport. The viewfinder will be
   /// initially set up to show world coordinates (0, 0) at the center of the
   /// viewport.
-  factory CameraComponent.withFixedResolution({
+  CameraComponent.withFixedResolution({
     required double width,
     required double height,
-    Viewfinder? viewfinder,
     World? world,
+    Viewfinder? viewfinder,
     Component? backdrop,
     List<Component>? hudComponents,
-  }) {
-    return CameraComponent(
-      world: world,
-      viewport: FixedResolutionViewport(resolution: Vector2(width, height))
-        ..addAll(hudComponents ?? []),
-      viewfinder: viewfinder ?? Viewfinder(),
-      backdrop: backdrop,
-    );
-  }
+  }) : this(
+          world: world,
+          viewport: FixedResolutionViewport(resolution: Vector2(width, height)),
+          viewfinder: viewfinder ?? Viewfinder(),
+          backdrop: backdrop,
+          hudComponents: hudComponents,
+        );
 
   /// The [viewport] is the "window" through which the game world is observed.
   ///