Support nested Matrix clients via the widget API (#2473)

* WIP RoomWidgetClient

* Wait for the widget API to become ready before backfilling

* Add support for sending user-defined encrypted to-device messages

This is a port of the same change from the robertlong/group-call branch.

* Fix tests

* Emit an event when the client receives TURN servers

* Expose the method in MatrixClient

* Override the encryptAndSendToDevices method

* Add support for TURN servers in embedded mode and make calls mostly work

* Don't put unclonable objects into VoIP events

RoomWidget clients were unable to send m.call.candidate events, because
the candidate objects were not clonable for use with postMessage.
Converting such objects to their canonical JSON form before attempting
to send them over the wire solves this.

* Fix types

* Fix more types

* Fix lint

* Upgrade matrix-widget-api

* Save lockfile

* Untangle dependencies to fix tests

* Add some preliminary tests

* Fix tests

* Fix indirect export

* Add more tests

* Resolve TODOs

* Add queueToDevice to RoomWidgetClient

src/matrix.ts

@@ -1,5 +1,5 @@
 /*
-Copyright 2015-2021 The Matrix.org Foundation C.I.C.
+Copyright 2015-2022 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -14,14 +14,16 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { WidgetApi } from "matrix-widget-api";
+
 import { MemoryCryptoStore } from "./crypto/store/memory-crypto-store";
 import { MemoryStore } from "./store/memory";
 import { MatrixScheduler } from "./scheduler";
 import { MatrixClient, ICreateClientOpts } from "./client";
-import { DeviceTrustLevel } from "./crypto/CrossSigning";
-import { ISecretStorageKeyInfo } from "./crypto/api";
+import { RoomWidgetClient, ICapabilities } from "./embedded";
 
 export * from "./client";
+export * from "./embedded";
 export * from "./http-api";
 export * from "./autodiscovery";
 export * from "./sync-accumulator";
@@ -51,6 +53,7 @@ export * from './@types/requests';
 export * from './@types/search';
 export * from './models/room-summary';
 export * as ContentHelpers from "./content-helpers";
+export type { ICryptoCallbacks } from "./crypto"; // used to be located here
 export { createNewMatrixCall } from "./webrtc/call";
 export type { MatrixCall } from "./webrtc/call";
 export {
@@ -108,27 +111,17 @@ export function setCryptoStoreFactory(fac) {
     cryptoStoreFactory = fac;
 }
 
-export interface ICryptoCallbacks {
-    getCrossSigningKey?: (keyType: string, pubKey: string) => Promise<Uint8Array>;
-    saveCrossSigningKeys?: (keys: Record<string, Uint8Array>) => void;
-    shouldUpgradeDeviceVerifications?: (
-        users: Record<string, any>
-    ) => Promise<string[]>;
-    getSecretStorageKey?: (
-        keys: {keys: Record<string, ISecretStorageKeyInfo>}, name: string
-    ) => Promise<[string, Uint8Array] | null>;
-    cacheSecretStorageKey?: (
-        keyId: string, keyInfo: ISecretStorageKeyInfo, key: Uint8Array
-    ) => void;
-    onSecretRequested?: (
-        userId: string, deviceId: string,
-        requestId: string, secretName: string, deviceTrust: DeviceTrustLevel
-    ) => Promise<string>;
-    getDehydrationKey?: (
-        keyInfo: ISecretStorageKeyInfo,
-        checkFunc: (key: Uint8Array) => void,
-    ) => Promise<Uint8Array>;
-    getBackupKey?: () => Promise<Uint8Array>;
+function amendClientOpts(opts: ICreateClientOpts | string): ICreateClientOpts {
+    if (typeof opts === "string") opts = { baseUrl: opts };
+
+    opts.request = opts.request ?? requestInstance;
+    opts.store = opts.store ?? new MemoryStore({
+        localStorage: global.localStorage,
+    });
+    opts.scheduler = opts.scheduler ?? new MatrixScheduler();
+    opts.cryptoStore = opts.cryptoStore ?? cryptoStoreFactory();
+
+    return opts;
 }
 
 /**
@@ -154,19 +147,17 @@ export interface ICryptoCallbacks {
  * @see {@link module:client.MatrixClient} for the full list of options for
  * <code>opts</code>.
  */
-export function createClient(opts: ICreateClientOpts | string) {
-    if (typeof opts === "string") {
-        opts = {
-            "baseUrl": opts,
-        };
-    }
-    opts.request = opts.request || requestInstance;
-    opts.store = opts.store || new MemoryStore({
-        localStorage: global.localStorage,
-    });
-    opts.scheduler = opts.scheduler || new MatrixScheduler();
-    opts.cryptoStore = opts.cryptoStore || cryptoStoreFactory();
-    return new MatrixClient(opts);
+export function createClient(opts: ICreateClientOpts | string): MatrixClient {
+    return new MatrixClient(amendClientOpts(opts));
+}
+
+export function createRoomWidgetClient(
+    widgetApi: WidgetApi,
+    capabilities: ICapabilities,
+    roomId: string,
+    opts: ICreateClientOpts | string,
+): MatrixClient {
+    return new RoomWidgetClient(widgetApi, capabilities, roomId, amendClientOpts(opts));
 }
 
 /**