MediaHandler Tests (#2646)
* MediaHandler Tests, part 1
Haven't got through all the methods yet
For https://github.com/vector-im/element-call/issues/544
* Didn't need these in the end
* Rest of the media handler tests
* getUserMediaStream takes args
* use mockResolvedValue
* Add .off & reuse the mock we already made
* Re-use mock handler again
* Move updateLocalUsermediaStream to beforeEach
* add .off
* Add types
* Add more .offs
