Add flag for media action button placement update

This will flag SysUI's implementation of the proposed Media3 API for action button placement preferences

Bug: 360196209
Change-Id: I0c51727cd77a57e4a3d889842612d7c977ae5071
Flag: com.android.systemui.media_controls_button_media3_placement
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 0b18110..a984b7d 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -1148,6 +1148,13 @@
 }
 
 flag {
+  name: "media_controls_button_media3_placement"
+  namespace: "systemui"
+  description: "Use media3 API for action button placement preferences"
+  bug: "360196209"
+}
+
+flag {
   name: "media_controls_drawables_reuse"
   namespace: "systemui"
   description: "Re-use created media drawables for media controls"