Spatializer: process callbacks in separate thread

Add a Looper and Handler to process events from the engine
and pose controler callback to avoid cross mutex deadlocks.

Bug: 188502620
Test: manual test with mock spatializer
Change-Id: I1342602259b147727c704ad7bbeb1b3a68c7b231
Merged-In: I1342602259b147727c704ad7bbeb1b3a68c7b231
diff --git a/services/audiopolicy/service/Android.bp b/services/audiopolicy/service/Android.bp
index a73e270..834478f 100644
--- a/services/audiopolicy/service/Android.bp
+++ b/services/audiopolicy/service/Android.bp
@@ -49,6 +49,7 @@
         "libsensorprivacy",
         "libshmemcompat",
         "libutils",
+        "libstagefright_foundation",
         "audioclient-types-aidl-cpp",
         "audioflinger-aidl-cpp",
         "audiopolicy-aidl-cpp",