Convert call test to TypeScript

Typescript tests basically just appear to work, apart from needing
the jest types imported so the typescript checker knows what's what.

DConvert the webrtc test to typescript, which actually mostly just
serves to point out that we're not mocking the whole of `document`,
but oh well.

spec/unit/webrtc/call.spec.ts

@@ -58,10 +58,13 @@ const DUMMY_SDP = (
 );
 
 class MockRTCPeerConnection {
+    localDescription: RTCSessionDescription;
+
     constructor() {
         this.localDescription = {
             sdp: DUMMY_SDP,
-            type: '',
+            type: 'offer',
+            toJSON: function() {},
         };
     }
 
@@ -91,6 +94,7 @@ describe('Call', function() {
 
         global.navigator = {
             mediaDevices: {
+                // @ts-ignore Mock
                 getUserMedia: () => {
                     return {
                         getTracks: () => [],
@@ -102,14 +106,18 @@ describe('Call', function() {
         };
 
         global.window = {
+            // @ts-ignore Mock
             RTCPeerConnection: MockRTCPeerConnection,
+            // @ts-ignore Mock
             RTCSessionDescription: {},
+            // @ts-ignore Mock
             RTCIceCandidate: {},
             getUserMedia: {},
         };
+        // @ts-ignore Mock
         global.document = {};
 
-        client = new TestClient();
+        client = new TestClient("@alice:foo", "somedevice", "token", undefined, {});
         call = new MatrixCall({
             client: client.client,
             roomId: '!foo:bar',