Add tracing subscriber for ATrace

A simple subscriber that forwards calls to ATrace. It is not optimized,
the purpose of this implementation is to have a working starting point
to test and benchmark.

Tests follow the same pattern as the main libatrace_rust but we had to
copy the global mock helpers because the mocked methods are different.

Bug: 293435349
Test: atest
Test: manually uploaded and captured a trace

Change-Id: Ibce802ec28159366d5d58550b105e9cd9546fded
4 files changed