union support for NDK backend

Generated class for AIDL union for NDK backend is similar to the one for
C++ backend. Differences are
- not inheriting Parcelable, but has similar read/write methods
- not having comparison operators.

Bug: 150948558
Bug: 170784707
Test: aidl_unittests / aidl_integration_test
Test: CtsNdkBinderTestCases
Change-Id: Ib7f9265d7664ae98b9edd4a40d50351180c9a4d2
5 files changed