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
diff --git a/audio/aidl/default/Stream.cpp b/audio/aidl/default/Stream.cpp
index 251dea0..215de94 100644
--- a/audio/aidl/default/Stream.cpp
+++ b/audio/aidl/default/Stream.cpp
@@ -110,10 +110,12 @@
     if (isConnected) {
         reply->observable.frames = mFrameCount;
         reply->observable.timeNs = ::android::elapsedRealtimeNano();
-    } else {
-        reply->observable.frames = StreamDescriptor::Position::UNKNOWN;
-        reply->observable.timeNs = StreamDescriptor::Position::UNKNOWN;
+        if (auto status = mDriver->getPosition(&reply->observable); status == ::android::OK) {
+            return;
+        }
     }
+    reply->observable.frames = StreamDescriptor::Position::UNKNOWN;
+    reply->observable.timeNs = StreamDescriptor::Position::UNKNOWN;
 }
 
 void StreamWorkerCommonLogic::populateReplyWrongState(