access::swap
access::swap

Summary:
An invoker suite to free function swap, with std::swap in scope.

Then, `std::is_swappable_v<A, B>` is equivalent to `folly::is_invocable_v<folly::access::swap, A, V>`, &c. for related traits.

Reviewed By: Mizuchi

Differential Revision: D34836697

fbshipit-source-id: f8411794e571ae61d9610802162f2667e90b041c

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