Update PROPERTY_HIGH_DEF_AUDIO API docs.

Make it more clear that the intention of the property is to convey whether
a call is high definition on the UI or not, and NOT to report the actual
audio codec in use.

Test: Build
Bug: 78550833
Change-Id: Id002cd1c9cc1d5aea6f8d9ab4e3d99956b7c42b2
diff --git a/telecomm/java/android/telecom/Call.java b/telecomm/java/android/telecom/Call.java
index 08bc9bc..daa09f5 100644
--- a/telecomm/java/android/telecom/Call.java
+++ b/telecomm/java/android/telecom/Call.java
@@ -397,7 +397,19 @@
         public static final int PROPERTY_WIFI = 0x00000008;
 
         /**
-         * Call is using high definition audio.
+         * When set, the UI should indicate to the user that a call is using high definition
+         * audio.
+         * <p>
+         * The underlying {@link ConnectionService} is responsible for reporting this
+         * property.  It is important to note that this property is not intended to report the
+         * actual audio codec being used for a Call, but whether the call should be indicated
+         * to the user as high definition.
+         * <p>
+         * The Android Telephony stack reports this property for calls based on a number
+         * of factors, including which audio codec is used and whether a call is using an HD
+         * codec end-to-end.  Some mobile operators choose to suppress display of an HD indication,
+         * and in these cases this property will not be set for a call even if the underlying audio
+         * codec is in fact "high definition".
          */
         public static final int PROPERTY_HIGH_DEF_AUDIO = 0x00000010;