Enhancement: Deprecate winrt::resume_on_signal

Some of the behaviors of winrt::resume_on_signal are problematic, undocumented, and severely misunderstood. Consider deprecate winrt::resume_on_signal first, and if someone truly needs it, consider writing a replacement.
See https://github.com/microsoft/cppwinrt/issues/1329 and https://github.com/YexuanXiao/cppwinrtplus/issues/5.