Implement call hold

Currently just by adding /holdcall and /unholdcall slash commands

The only place the hold status of the call is currently represented
is when the call is a voice call and you're viewing a different room:
it's not wired up when you're viewing the room because that currently
uses the room status bar which it won't do with the new UI.

Also convert VideoFeed to typescript, and remove videoview because
it essentially just managed the fullscreen functionality, but we'll
want and 'on hold' representation (and probably chrome for hagnup etc)
in the fullscreen UI too, so let's just make CallView the thing that
gets fullscreened.

src/SlashCommands.tsx

@@ -46,6 +46,7 @@ import { EffectiveMembership, getEffectiveMembership, leaveRoomBehaviour } from
 import SdkConfig from "./SdkConfig";
 import SettingsStore from "./settings/SettingsStore";
 import {UIFeature} from "./settings/UIFeature";
+import CallHandler from "./CallHandler";
 
 // XXX: workaround for https://github.com/microsoft/TypeScript/issues/31816
 interface HTMLInputEvent extends Event {
@@ -1039,6 +1040,32 @@ export const Commands = [
         },
         category: CommandCategories.actions,
     }),
+    new Command({
+        command: "holdcall",
+        description: _td('Places the call in the current room on hold'),
+        category: CommandCategories.other,
+        runFn: function(roomId, args) {
+            const call = CallHandler.sharedInstance().getCallForRoom(roomId);
+            if (!call) {
+                return reject("No active call in this room");
+            }
+            call.setRemoteOnHold(true);
+            return success();
+        },
+    }),
+    new Command({
+        command: "unholdcall",
+        description: _td('Takes the call in the current room off hold'),
+        category: CommandCategories.other,
+        runFn: function(roomId, args) {
+            const call = CallHandler.sharedInstance().getCallForRoom(roomId);
+            if (!call) {
+                return reject("No active call in this room");
+            }
+            call.setRemoteOnHold(false);
+            return success();
+        },
+    }),
 
     // Command definitions for autocompletion ONLY:
     // /me is special because its not handled by SlashCommands.js and is instead done inside the Composer classes