Expose various Telecom constants

Expose constants in Telecom that are being used in Telephony.
Note -- nothing is exposed here -- it's a modified cherry pick from
internal where all the APIs have been rehidden.

Bug: 146834818
Test: NA
Change-Id: Ib5cf76183edced3eeffbca87a7c980a85288f937
Merged-In: Ib5cf76183edced3eeffbca87a7c980a85288f937
diff --git a/telecomm/java/android/telecom/PhoneAccount.java b/telecomm/java/android/telecom/PhoneAccount.java
index 6ae4a08..768c8ee 100644
--- a/telecomm/java/android/telecom/PhoneAccount.java
+++ b/telecomm/java/android/telecom/PhoneAccount.java
@@ -82,8 +82,10 @@
     public static final String EXTRA_CALL_SUBJECT_CHARACTER_ENCODING =
             "android.telecom.extra.CALL_SUBJECT_CHARACTER_ENCODING";
 
-     /**
-     * Indicating flag for phone account whether to use voip audio mode for voip calls
+    /**
+     * Boolean {@link PhoneAccount} extras key (see {@link PhoneAccount#getExtras()}) which
+     * indicates that all calls from this {@link PhoneAccount} should be treated as VoIP calls
+     * rather than cellular calls.
      * @hide
      */
     public static final String EXTRA_ALWAYS_USE_VOIP_AUDIO_MODE =