Add binder transaction size tracing

As binder transaction latency depends heavily on message size, it's
useful to trace the sizes as well.

I'll submit a change to catapult (systrace visualizer) to add the size
information to the binder transaction events as well.

Test: ran systrace.py ... binder_driver, looked at captured data
Test: mm in $ANDROID_BUILD_TOP
Bug: 78137932
Change-Id: I07774ac6664b03d9ebc563723831d84313821eb0