* 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`
