Use native video call picture in picture! (#3190)

* Use native video call picture in picture!

* Handle isSupported, isPossible and web view errors.

* Use new canEnterPip method.

* Hide a room's Call button when already joined to the call.

* Tweak feature flag description.

* PR comments.

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/DeveloperOptionsScreenModels.swift

@@ -53,6 +53,7 @@ protocol DeveloperOptionsProtocol: AnyObject {
     var elementCallBaseURLOverride: URL? { get set }
     var fuzzyRoomListSearchEnabled: Bool { get set }
     var pinningEnabled: Bool { get set }
+    var elementCallPictureInPictureEnabled: Bool { get set }
 }
 
 extension AppSettings: DeveloperOptionsProtocol { }

ElementX/Sources/Screens/Settings/DeveloperOptionsScreen/View/DeveloperOptionsScreen.swift

@@ -61,6 +61,11 @@ struct DeveloperOptionsScreen: View {
                     .autocorrectionDisabled(true)
                     .autocapitalization(.none)
                     .foregroundColor(URL(string: elementCallBaseURLString) == nil ? .red : .primary)
+                
+                Toggle(isOn: $context.elementCallPictureInPictureEnabled) {
+                    Text("Picture in Picture support")
+                    Text("Requires an Element Call deployment with support for signalling PiP availability.")
+                }
             }
             
             Section {