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/test-utils/test-utils.ts

@@ -60,6 +60,8 @@ import MatrixClientBackedSettingsHandler from "../../src/settings/handlers/Matri
  * TODO: once the components are updated to get their MatrixClients from
  * the react context, we can get rid of this and just inject a test client
  * via the context instead.
+ *
+ * See also `getMockClientWithEventEmitter` which does something similar but different.
  */
 export function stubClient(): MatrixClient {
     const client = createTestClient();