invoke_type members for free- and member-invoke traits containers
invoke_type members for free- and member-invoke traits containers

Summary:
[Folly] `invoke_type` members for free- and member-invoke traits containers.

Usable as:

```
FOLLY_CREATE_FREE_INVOKE_TRAITS(swap_invoke_traits, swap, std);
// ...
swap_invoke_traits::invoke_type my_swap;
my_swap(obj1, obj2);

Reviewed By: aary

Differential Revision: D8670799

fbshipit-source-id: 0c24912721aa20ca9647261e24ed3eb0e340ab20

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly