Port ConcurrencyTests from TAEF (#3086)

* Add ConcurrencyTests

* Make ConcurrencyTests compatible with TAEF

* Use test PCH in concurrency tests

* Fix include header

* Ignore unused code warnings on WINML_SKIP_TEST

* Remove BOM

* Remove conflicting namespace in older SDK

* Refactor duplicate code

* Fix unused DELAYLOAD

* Fix unused DELAYLOAD

* Remove link to internal bug

* Address code style fixes

* Add new concurrency tests