New CryptoApi.getDeviceVerificationStatus api (#3287)

* Element-R: implement `{get,set}TrustCrossSignedDevices`

A precursor to https://github.com/vector-im/element-web/issues/25092

* Pull out new `DeviceVerificationStatus`

Define a new base class to replace `DeviceTrustLevel`. The intention is to have
a cleaner interface which is easier to expose from the new crypto impl

* Define, and implement, a new `CryptoApi.getDeviceVerificationStatus`

This is similar to `checkDeviceTrust`, which we're deprecating, but:
 * is `async`, meaning we can implement it in Rust
 * Returns a `DeviceVerificationStatus` instead of a `DeviceTrustLevel`
 * Returns `null` rather than "not verified" if the device is unknown

* add some tests

* Export DeviceVerificationStatus as a proper class

... so that we can instantiate it in tests

src/matrix.ts

@@ -63,6 +63,7 @@ export type { MatrixCall } from "./webrtc/call";
 export { GroupCallEvent, GroupCallIntent, GroupCallState, GroupCallType } from "./webrtc/groupCall";
 export type { GroupCall } from "./webrtc/groupCall";
 export type { CryptoApi } from "./crypto-api";
+export { DeviceVerificationStatus } from "./crypto-api";
 export { CryptoEvent } from "./crypto";
 
 let cryptoStoreFactory = (): CryptoStore => new MemoryCryptoStore();