Element-R: wire up device lists

[richvdh]

We need to implement MatrixClient.downloadKeys and MatrixClient.getStoredDevicesForUser. This is used to populate the device list in the right panel, as well as determining whether we should use an encrypted room when starting DMs with a user (#24429).

Broadly, we need to:

• decide if we are tracking a user's devices by calling OlmMachine.trackedUsers.
• If we are, call OlmMachine.getUserDevices() and translate the returned info into an IDevice.
• If we are not (and downloadUncached is set, see below), hit /_matrix/client/v3/keys/query to download the device list, and translate the result of that into an Device (new Device model from the js-sdk).

I'd like to take the opportunity to clean up the API a bit here, so I'd propose adding a single method to CryptoApi:

/**
 * Get the device information for the given list of users.
 *
 * @param userIds - The users to fetch.
 * @param downloadUncached - If true, download the device list for users whose device list we are not
 *    currently tracking. Defaults to false, in which case such users will not appear at all in the result map.
 *
 * @returns A map `userId->deviceId->{@link Device}`.
 */
getUserDeviceInfo(
    userIds: string[],
    downloadUncached?: boolean,
): Promise<Map<string, Map<string, Device>>>;

For legacy Crypto, we implement this with a thin shim onto the existing Crypto.downloadKeys and Crypto.getStoredDevicesForUser. We also replace MatrixClient.downloadKeys and MatrixClient.getStoredDevicesForUser with thin shims onto CryptoApi.getUserDeviceInfo.

The forceDownload parameter of MatrixClient.downloadKeys is used in exactly one place (when populating the right panel), and I think we should quietly ignore it: the magical "fix bugs in my caching logic by skipping the cache" logic does more harm than good.

• Element-R: wire up device lists matrix-org/matrix-js-sdk#3272
• Element-R: Stub findVerificationRequestDMInProgress and getStoredCrossSigningForUser matrix-org/matrix-js-sdk#3315
• Element-R: Populate device list for right-panel matrix-org/matrix-react-sdk#10671
• Element-R: Starting a DMs with a user matrix-org/matrix-react-sdk#10673

[richvdh]

some untested work on the translation to an IDevice in matrix-org/matrix-js-sdk@develop...rav/element-r/device_list_work