libbinder: detach ParcelFileDescriptor comm

Now that ParcelFileDescriptors are being exposed in the NDK, we need
to provide the correct behavior when these are expected to be used
with comms.

- ideally, this code would be refactored to be inside of
  ParcelFileDescriptor.(cpp|h), however many places in the codebase
  call this function directly, so I'm leaving it in Parcel.cpp for now
- BIG_ENDIAN path can't be tested, but it's being added to be
  consistent with writeInplace.

Change-Id: I93b9cede757c4423c49bc117c4d96c5a501de6f4
Fixes: 115607973
Test: android.binder.cts