Remove experimental coroutines support by sylveon · Pull Request #1521 · microsoft/cppwinrt

@sylveon

Replace CppWinRTEnableLegacyCoroutines with CppWinRTEnableCpp17Coroutines

Remove base_coroutine_system_winui.h, hasn't worked since PR 0.8

Support and test building with no coroutines

Remove implementation selection machinery

@sylveon

@DefaultRyan

Add error message for missing coroutine support in C++.

@sylveon

@sylveon

DefaultRyan

DefaultRyan