Action.cpp: replace a reference with a shared_ptr

Action.cpp: replace a reference with a shared_ptr

Replace the member reference to FuncRequest in Action.cpp with a
shared_ptr. Compared to copying the FuncRequest, the shared_ptr has two
advantages:

* Recreating the menu each time creates a lot of new actions, so we avoid a lot
  of copies.

* FuncRequest can remain forward-declared in Action.h.