Kill off references to deprecated getStoredDevice and getStoredDevicesForUser (#11152)

* 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`

test/components/views/right_panel/UserInfo-test.tsx

@@ -160,7 +160,6 @@ beforeEach(() => {
         credentials: {},
         setPowerLevel: jest.fn(),
         downloadKeys: jest.fn(),
-        getStoredDevicesForUser: jest.fn(),
         getCrypto: jest.fn().mockReturnValue(mockCrypto),
         getStoredCrossSigningForUser: jest.fn(),
     } as unknown as MatrixClient);