Implement Rust backend for AIDL compiler

New backend for Rust compatible with libbinder_rs, based on the
existing C++/Java/NDK backends. Includes support for aidl_interface.

Bug: 161559780
Test: atest aidl_unittests
Change-Id: I54353421320f1228f16d22c2d2b60cd8add8b6f9
23 files changed