Support iOS <13 macOS <10.15 by using OpenCombine? Maybe?

[helje5]

Not sure it makes sense, but it would be really nice to be able to use all those in older OS'es.

[helje5]

Example of a Package.swift including OpenCombine conditionally: https://github.com/SwiftWebUI/SwiftWebUI/blob/develop/Package.swift

OK, that doesn't work in this case. Needs to be selected via runtime (i.e. @available)