Test for asserted identity

This is out first CallHandler test(!) Switches react-sdk to use
createCall on the client object so we can stub this out in the test.
Add a bunch more stubs to the test client.

There's more stuff in this test that has scope to be used more
widely, like waiting for a certain dispatch and mocking out rooms
with particular sets of users in them: we could consider moving these
out to test utils if we wanted.

test/test-utils.js

@@ -64,6 +64,11 @@ export function createTestClient() {
         getRoomIdForAlias: jest.fn().mockResolvedValue(undefined),
         getRoomDirectoryVisibility: jest.fn().mockResolvedValue(undefined),
         getProfileInfo: jest.fn().mockResolvedValue({}),
+        getThirdpartyProtocols: jest.fn().mockResolvedValue({}),
+        getClientWellKnown: jest.fn().mockReturnValue(null),
+        supportsVoip: jest.fn().mockReturnValue(true),
+        getTurnServersExpiry: jest.fn().mockReturnValue(2^32),
+        getThirdpartyUser: jest.fn().mockResolvedValue([]),
         getAccountData: (type) => {
             return mkEvent({
                 type,