Add comparison operators for ParcelFileDescriptor

With I9f833d0c1a91c8ec72b1cd80007b2f2c09205435, the AIDL C++ compiler
creates comparison operators for structured parcelables. That implies
that each member of a structure parcelable should also has the
comparison operators defined. That assumption breaks when
ParcelFileDescriptor is used as a member, because ParcelFileDescriptor
does not define the comparison operators. Fixing the issue by adding
them, which delegates the comparisons to the internal unique_fd field.

Bug: 143712561
Test: apply ag/9646381 and `m libincremental_aidl-cpp`

Change-Id: Ibc11eafa268e03dc30f321d692f43c0a99a6af1c