@Sendable func on Sendable types

Using Swift
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2

This pitch proposes that @Sendable func should be inferred on types that conform to Sendable.

But methods of a nominal type cannot capture anything but the object instance itself. Thus, the proposed simplifications are:

  1. the inference of @Sendable on all methods of a type that conforms to Sendable.
  2. the inference of @Sendable on all non-local functions.
  3. the prohibition of marking a method @Sendable if the object type does not conform to Sendable.