aaudio: steal exclusive streams

An app (B) that asks for an exclusive stream can steal
an exclusive stream from an earlier app (A).
App B will be given the MMAP resource as a SHARED stream.
The stream for app A will be disconnected and released
by the service.
If app A reopens a stream then it will get a SHARED
stream.

The order of the opening of the streams is controlled by using a
recursive_mutex in AAudioService::openStream().

Bug: 129846760
Test: media/libaaudio/tests/test_steal_exclusive.cpp
Test: also
Test: Launch AudioTroubleMaker. It should say "EXCLUSIVE".
Test: Press Home button.
Test: Siren sound from AudioTroubleMaker should continue.
Test: Launch OboeTester
Test: TEST OUTPUT, then Open, Start
Test: You should get an MMAP SHARED stream on Pixel.
Test: Go back to AudioTroubleMaker. It should say "SHARED".
Change-Id: I7f8339d8ed62546520a9b46ed398418b41ca2832
diff --git a/services/oboeservice/AAudioServiceEndpointMMAP.cpp b/services/oboeservice/AAudioServiceEndpointMMAP.cpp
index af2710d..9dab770 100644
--- a/services/oboeservice/AAudioServiceEndpointMMAP.cpp
+++ b/services/oboeservice/AAudioServiceEndpointMMAP.cpp
@@ -229,7 +229,7 @@
 }
 
 aaudio_result_t AAudioServiceEndpointMMAP::close() {
-    if (mMmapStream != 0) {
+    if (mMmapStream != nullptr) {
         // Needs to be explicitly cleared or CTS will fail but it is not clear why.
         mMmapStream.clear();
         // Apparently the above close is asynchronous. An attempt to open a new device