Previously, we would get two copies, one accessing the pointee and one
when we pass the pointee as a method as the implicit self argument.
These copies are unsafe as they might introduce slicing. When
addressable paramaters features are enabled, we no longer make these
copies for the standard STL types. Custom smart pointers can replicate
this by making the lifetime dependency between the implicit object
parameter and the returned reference of operator* explicit via a
lifetime annotation.
rdar://154213694&128293252&112690482
C++ code can return values that depend on the storage that backs the
references that were passed in as argument. Thus, swift should not
introdue temporary copies of that storage before invoking those
functions as they could result in lifetime issues.
