Windows 10 Version 1903 - December 2020 Samples Update

* AudioCreation: Add microphone selection to scenario 2
* BarcodeScanner: Add missing namespace qualifier #1253
* HttpClient: Take advantage of C++/WinRT cancellation feature microsoft/cppwinrt#721
* LockScreenApps: Provide workaround for Settings app issue #1249
* MediaTranscoding: Explicitly set the H.264 encoder level to 5.2 when needed
* MobileBroadband: Fix order of parameters #1255
* C++/WinRT template: Use angle brackets for C++/WinRT headers #1231
* Fix broken links and typos in README files #1235 #1245 #1256
* New samples: WebSocket (C++WinRT)