Send the Audio Usage down from AudioPolicyManager

Store audioUsgae in AudioAttributes and send it down to
AudioFlinger::openOutput_l. Then extract audioUsage and store in
SourceMetadata to pass it down to the HAL layer.

Bug: 297875432
Test: Add a fake audio usage in attribute in AudioFlinger::openoutput(), then test by checking the log message. The fake usage does get pass down to the DeviceHalAidl::openOutputStream().
Flag: EXEMPT bugfix
Change-Id: Ic9a739f1de50485304187be5c4b603955afabbf8