Implementing support for HIDL native handles in Java

This change implements the equivalent of the C++ native_handle_t type in
Java. Similar to the C++ type, the NativeHandle class wraps an arraylist
of FileDescriptor objects, along with a raw data stream (integer array).

Bug: 35098567
Test: Ran m, hidl_test (C++ and Java). Functionality tests are included
in a separate CL.

Change-Id: Ic53f9a49ae17ce5708577a586230126ab0e222c7