audio: Add StreamDescriptor.frameSizeBytes

This field indicates the frame size and is filled by
the HAL module, so that the client does not have
to calculate it.

As a side effect, in the VTS code, a StreamContext can
now be created solely from a StreamDescriptor.

Added unit tests for the functions from Utils.

Bug: 205884982
Test: atest libaudioaidlcommon_test
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Ief836b8b2d35bacb1f9778e2462d540554149d7f