Fix device selection never completing in widget mode

By reinstating some of the code from the full mesh branch that was there to handle this

src/media-utils.ts

@@ -0,0 +1,32 @@
+/*
+Copyright 2022 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * Finds a media device with label matching 'deviceName'
+ * @param deviceName The label of the device to look for
+ * @param devices The list of devices to search
+ * @returns A matching media device or undefined if no matching device was found
+ */
+export async function findDeviceByName(
+  deviceName: string,
+  kind: MediaDeviceKind,
+  devices: MediaDeviceInfo[]
+): Promise<string | undefined> {
+  const deviceInfo = devices.find(
+    (d) => d.kind === kind && d.label === deviceName
+  );
+  return deviceInfo?.deviceId;
+}