Add widget actions for joining and leaving calls and switching layouts

These actions are processed lazily to ensure that even if the app takes a while to start up, they won't be missed.

src/room/useRoomParams.ts

@@ -24,6 +24,9 @@ export interface RoomParams {
   // Whether the app is running in embedded mode, and should keep the user
   // confined to the current room
   isEmbedded: boolean;
+  // Whether the app should pause before joining the call until it sees an
+  // io.element.join widget action, allowing it to be preloaded
+  preload: boolean;
   // Whether to hide the room header when in a call
   hideHeader: boolean;
   // Whether to start a walkie-talkie call instead of a video call
@@ -77,6 +80,7 @@ export const getRoomParams = (
     roomId: getParam("roomId"),
     viaServers: getAllParams("via"),
     isEmbedded: hasParam("embed"),
+    preload: hasParam("preload"),
     hideHeader: hasParam("hideHeader"),
     isPtt: hasParam("ptt"),
     e2eEnabled: getParam("enableE2e") !== "false", // Defaults to true