* Use new `CryptoEvent.VerificationRequestReceived` event
https://github.com/matrix-org/matrix-js-sdk/pull/3514 deprecates
`CryptoEvent.VerificationRequest` in favour of
`CryptoEvent.VerificationRequestReceived`. Use the new event.
* Factor out `getDeviceCryptoInfo` function
I seem to be writing this logic several times, so let's factor it out.
* Factor out `getUserDeviceIds` function
Another utility function
* VerificationRequestToast: `getStoredDevice` -> `getDeviceCryptoInfo`
* SlashCommands: `getStoredDevice` -> `getDeviceCryptoInfo`
* MemberTile: `getStoredDevicesForUser` -> `getUserDeviceIds`
* Remove redundant mock of `getStoredDevicesForUser`
* Update references to `VerificationRequestEvent`
* Update references to `Phase`
* update references to legacy `PHASE_*` constants
* Replace `request.canAccept` with `canAcceptVerificationRequest`
* Replace `VerificationRequest` with the interface throughout
* Minor strict type fixes
* Add a couple of tests
* Use new `VerificationRequest.getQRCodeBytes()`
* Use new `VerificationRequest.otherDeviceId`
* Remove references to `VerificationRequest.channel`
* Replace references to `VerificationRequest.{requesting,receiving}UserId`
Normally these are guarded by `request.initiatedByMe` so we can trivially
replace it with `request.otherUserId` or `client.getUserId()`. In one place we
actually need to apply some logic.
* increase test coverage
* Even more test coverage
* Even more test coverage
