refactor: adopt UIScene lifecycle

feat: add initial support for pip

feat: add setting toggle for pip

fix: let os handle invokation of pip which is more reliable

fix: UIScene compatibility with airplay

fix: black screen on external display when on app view and streaming

fix: incorrect window size when launched directly on external display

fix: wrong resolution shown in settings when in stream session

Enable gamemode flag for iOS18+

Explicitly enters pip mode when in background

Limelight/SceneDelegate.h

@@ -0,0 +1,12 @@
+#import <UIKit/UIKit.h>
+
+@interface SceneDelegate : UIResponder <UIWindowSceneDelegate>
+
+@property (strong, nonatomic) UIWindow * window;
+
++ (void)setExternalDisplayRenderView:(UIView *)renderView;
++ (void)clearExternalDisplayRenderView;
+- (void)updatePreferredDisplayMode:(BOOL)streamActive withRenderView:(UIView *)renderView;
+
+@end
+