aaudio: refactor references to shared FIFO

Reduce passing of raw pointers.
Use shared_ptrs and unique_ptrs.
Simplify memory management.

Refactor FifoBuffer into two subclasses so that
the internal memory management is simpler.

Bug: 151650670
Test: OboeTester "TEST OUTPUT"
Test: disable EXCLUSIVE mode
Test: OboeTester "ECHO INPUT TO OUTPUT"
Test: disable INPUT EXCLUSIVE mode
Change-Id: I10981767f8719f3cc3525df211285c53219a7979
diff --git a/services/oboeservice/AAudioServiceEndpointPlay.cpp b/services/oboeservice/AAudioServiceEndpointPlay.cpp
index bda4b90..1603e41 100644
--- a/services/oboeservice/AAudioServiceEndpointPlay.cpp
+++ b/services/oboeservice/AAudioServiceEndpointPlay.cpp
@@ -100,9 +100,10 @@
                 {
                     // Lock the AudioFifo to protect against close.
                     std::lock_guard <std::mutex> lock(streamShared->getAudioDataQueueLock());
-
-                    FifoBuffer *fifo = streamShared->getAudioDataFifoBuffer_l();
-                    if (fifo != nullptr) {
+                    std::shared_ptr<SharedRingBuffer> audioDataQueue
+                            = streamShared->getAudioDataQueue_l();
+                    std::shared_ptr<FifoBuffer> fifo;
+                    if (audioDataQueue && (fifo = audioDataQueue->getFifoBuffer())) {
 
                         // Determine offset between framePosition in client's stream
                         // vs the underlying MMAP stream.