Figure out how to deal with community native modules and WinUI 3 support

[asklar]

Write up strategy for modules to either dual target, or convert to winappsdk.
Needs to also consider how winappsdk vs. UWP is surfaced in reactnative.directory.

[jonthysell]

@asklar Is this still something that makes sense for 0.69 or should it be moved to 0.70?