audio: rename virtualizer stage to spatializer

Use audio spatializer and spatialization instead of
virtualizer stage to reflect the name chosen for public APIs.

Bug: 188502620
Test: make
Change-Id: I7974c5b159722efd795e0b0b79ddbb0658c52034
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index b9801c2..33a83e1 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -1658,14 +1658,14 @@
     }
 };
 
-class VirtualizerStageThread : public MixerThread {
+class SpatializerThread : public MixerThread {
 public:
-    VirtualizerStageThread(const sp<AudioFlinger>& audioFlinger,
+    SpatializerThread(const sp<AudioFlinger>& audioFlinger,
                            AudioStreamOut* output,
                            audio_io_handle_t id,
                            bool systemReady,
                            audio_config_base_t *mixerConfig);
-            ~VirtualizerStageThread() override {}
+            ~SpatializerThread() override {}
 
             bool hasFastMixer() const override { return false; }