Add audio stream and usage for virtual assistant

New stream type: AUDIO_STREAM_ASSISTANT
This is intended to be used by a virtual assistant like
Google Assistant, Bixby, etc.

The audio stream has own volume alias and the volume
does not change by volume changes of other streams.

Bug: 123745215
Test: make
Change-Id: I3696d8fba32070954cc6a330574af8507fea7a74
diff --git a/audio/6.0/config/api/current.txt b/audio/6.0/config/api/current.txt
index ddd4d1c..0407d69 100644
--- a/audio/6.0/config/api/current.txt
+++ b/audio/6.0/config/api/current.txt
@@ -361,6 +361,7 @@
     method public String getRawName();
     enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_ACCESSIBILITY;
     enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_ALARM;
+    enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_ASSISTANT;
     enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_BLUETOOTH_SCO;
     enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_DTMF;
     enum_constant public static final audio.policy.configuration.V6_0.Stream AUDIO_STREAM_ENFORCED_AUDIBLE;
diff --git a/audio/6.0/config/audio_policy_configuration.xsd b/audio/6.0/config/audio_policy_configuration.xsd
index 3fab7dc..05c8ab4 100644
--- a/audio/6.0/config/audio_policy_configuration.xsd
+++ b/audio/6.0/config/audio_policy_configuration.xsd
@@ -551,6 +551,7 @@
             <xs:enumeration value="AUDIO_STREAM_DTMF"/>
             <xs:enumeration value="AUDIO_STREAM_TTS"/>
             <xs:enumeration value="AUDIO_STREAM_ACCESSIBILITY"/>
+            <xs:enumeration value="AUDIO_STREAM_ASSISTANT"/>
             <xs:enumeration value="AUDIO_STREAM_REROUTING"/>
             <xs:enumeration value="AUDIO_STREAM_PATCH"/>
         </xs:restriction>