Combine Interoperability: first iteration#776

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andersio wants to merge 6 commits intomasterfrom anders/combine-interop

+252

Commits on Apr 19, 2020

Convert any Signal, Producer or Property to a Combine publisher via publisher().
andersio
committed
Convert Combine publishers to producer via producer(). A few utilities.
andersio
committed
Update the availability annotations.
andersio
committed

Commits on Apr 26, 2020

Remove Cancellable conformances.
andersio
committed

Commits on Apr 27, 2020