Add declare_binder_enum! macro

This change moves all the AIDL enum boiler plate from the AIDL compiler
into libbinder_rs. The library now exports a declare_binder_enum! macro
that the compiler invokes.

Test: atest aidl_unittests aidl_integration_test
Change-Id: I32e6920851424ebbb3e17fee9a2f0e7c0fdf7f1d