audio: Add optional 'DriverInterface::getPosition' method.

This is a method which can be optionally implemented
by a stream in case it can provide more exact position,
for example by taking into account data in intermediate
buffers.

Implemented this method for StreamAlsa and StreamRemoteSubmix.

Bug: 264712385
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I392933f8f6b22d784726925199db00dcb0313648