Fix Electron type merging

This changes to an interface for Electron types so that other layers can merge
in further APIs as needed, such as the JS SDK.

src/@types/global.d.ts

@@ -39,18 +39,20 @@ declare global {
         matrixChat: ReturnType<Renderer>;
 
         // electron-only
-        electron: {
-            on(channel: ElectronChannel, listener: (event: Event, ...args: any[]) => void): void;
-            send(channel: ElectronChannel, ...args: any[]): void;
-        }
+        electron?: Electron;
 
         // opera-only
-        opera: any;
+        opera?: any;
 
         // https://developer.mozilla.org/en-US/docs/Web/API/InstallTrigger
         InstallTrigger: any;
     }
 
+    interface Electron {
+        on(channel: ElectronChannel, listener: (event: Event, ...args: any[]) => void): void;
+        send(channel: ElectronChannel, ...args: any[]): void;
+    }
+
     interface Navigator {
         // PWA badging extensions https://w3c.github.io/badging/
         setAppBadge?(count: number): Promise<void>;