Let EventBase::runInEventBaseThreadAndWait consume its argument

Let EventBase::runInEventBaseThreadAndWait consume its argument

Summary:
[Folly] Let `EventBase::runInEventBaseThreadAndWait` consume its argument.

Likewise `EventBase::runImmediatelyOrRunInEventBaseThreadAndWait`.

And enforce that the function is destructed before returning, so that, in the case of a wrapped lambda, all captured objects' destructors run before returning from the function.

Reviewed By: elsteveogrande

Differential Revision: D5994106

fbshipit-source-id: 816c9431a85a3d41e4fda321065614f4c18f0697