fix(ios): fit the picture to the window after a rotation

MPVKit's MoltenVK context reads the layer's drawableSize only when mpv
builds its video output and reports no resize after that (mpvkit/MPVKit#3).
A player opened upright and turned on its side went on drawing the upright
frame into a corner of the landscape drawable. The view now tells the
player when its drawable changes, and once the size settles the player
rebuilds mpv's output by turning the picture off and on, as the background
already does. The vid writes run in order off the main thread.

ios/ProtonStream/Player/PlayerView.swift

@@ -724,16 +724,18 @@ struct MpvView: UIViewRepresentable {
     let player: MpvPlayer
 
     func makeUIView(context _: Context) -> LayerView {
-        LayerView(layer: player.layer)
+        LayerView(player: player)
     }
 
     func updateUIView(_: LayerView, context _: Context) {}
 
     final class LayerView: UIView {
+        private let player: MpvPlayer
         private let video: CAMetalLayer
 
-        init(layer video: CAMetalLayer) {
-            self.video = video
+        init(player: MpvPlayer) {
+            self.player = player
+            video = player.layer
             super.init(frame: .zero)
             backgroundColor = .black
             video.removeFromSuperlayer()
@@ -759,6 +761,8 @@ struct MpvView: UIViewRepresentable {
             video.contentsScale = scale
             video.drawableSize = CGSize(width: bounds.width * scale, height: bounds.height * scale)
             CATransaction.commit()
+            // A new drawable is not enough on its own: mpv has to be told.
+            player.outputResized()
         }
 
         override func didMoveToWindow() {