audio: Add StreamWorker to aidl/common

This utility class has been copied from HIDL VTS.
It will be used both for the default implementation
and AIDL VTS, and might need modifications.

Bug: 205884982
Test: atest libaudioaidlcommon_test
Change-Id: I43b35b0c23ae45305dca66e15b60820cad19635e