[stdlib]: Handle nested binder txns

Previously, we made an assumption that any binder txns with children
were broken txns because binder txns are blocked until the reply.
This assumption isn't quite correct because binder txns are allowed to
nest.

In this example: thread A calls foo() on B and B calls bar() on A.

Thread A will receive bar() on the blocked thread. This is actually
quite common with Camera interactions with cameraserver.

Test: tools/diff_test_trace_processor.py out/android/trace_processor_shell --name-filter '.*binder.*'
Change-Id: Ia11e61e9ce5cdb80f6eb65e51eebef9eccc9a441