AudioService: Register MASTER_BALANCE/MONO observer for all users

Audioservice register content observer for MASTER_BALANCE/MONO at the time of initialization/boot up. Registration by default is only applicable for current user which in this case is primary user.
So even when audio balance/mono changes for secondary user, the callback
won't be received in audioservice and hence the settings update won't
have any effect on the audio output.

Bug: 339131898
Test: manual
- Validated that audio output balance and mono varies based on the settings in the secondary user
- atest AudioManagerTest
- atest AudioServiceTest

Change-Id: Ifce17d23e0dd0af61d6e27de7c7da629e9480e77
diff --git a/services/core/java/com/android/server/audio/AudioService.java b/services/core/java/com/android/server/audio/AudioService.java
index e9acce6..3024472 100644
--- a/services/core/java/com/android/server/audio/AudioService.java
+++ b/services/core/java/com/android/server/audio/AudioService.java
@@ -9448,9 +9448,9 @@
             mContentResolver.registerContentObserver(Settings.Global.getUriFor(
                 Settings.Global.DOCK_AUDIO_MEDIA_ENABLED), false, this);
             mContentResolver.registerContentObserver(Settings.System.getUriFor(
-                    Settings.System.MASTER_MONO), false, this);
+                    Settings.System.MASTER_MONO), false, this, UserHandle.USER_ALL);
             mContentResolver.registerContentObserver(Settings.System.getUriFor(
-                    Settings.System.MASTER_BALANCE), false, this);
+                    Settings.System.MASTER_BALANCE), false, this, UserHandle.USER_ALL);
 
             mEncodedSurroundMode = mSettings.getGlobalInt(
                     mContentResolver, Settings.Global.ENCODED_SURROUND_OUTPUT,