Improve DisconnectCause API for mainline.

As part of API feedback, improve the DisconnectCause API that was
formalized as part of Telecom mainline. This CL has some minor cleanup
around those suggestions (refer to the associated bug for more details).

Bug: 327030432
Bug: 311773409
Test: atest TelecomUnitTests, atest DataObjectUnitTests
Change-Id: Iac2b33131e225040f53156c00c5963d5f31f660b
diff --git a/src/com/android/services/telephony/DisconnectCauseUtil.java b/src/com/android/services/telephony/DisconnectCauseUtil.java
index c00adef..33bcfb5 100644
--- a/src/com/android/services/telephony/DisconnectCauseUtil.java
+++ b/src/com/android/services/telephony/DisconnectCauseUtil.java
@@ -119,8 +119,8 @@
             FlagsAdapter featureFlags) {
         Context context = PhoneGlobals.getInstance();
 
-        return new DisconnectCause.Builder()
-                .setCode(toTelecomDisconnectCauseCode(telephonyDisconnectCause, carrierConfig))
+        return new DisconnectCause.Builder(
+                toTelecomDisconnectCauseCode(telephonyDisconnectCause, carrierConfig))
                 .setLabel(toTelecomDisconnectCauseLabel(context, telephonyDisconnectCause,
                         telephonyPreciseDisconnectCause, carrierConfig, featureFlags))
                 .setDescription(toTelecomDisconnectCauseDescription(
@@ -140,8 +140,8 @@
      * {@link android.telecom.DisconnectCause} disconnect code.
      * @return The disconnect code as defined in {@link android.telecom.DisconnectCause}.
      */
-    private static int toTelecomDisconnectCauseCode(int telephonyDisconnectCause,
-            PersistableBundle carrierConfig) {
+    private static @DisconnectCause.DisconnectCauseCode int toTelecomDisconnectCauseCode(
+            int telephonyDisconnectCause, PersistableBundle carrierConfig) {
 
         // special case: some carriers determine what disconnect causes play the BUSY tone.
         // hence, must adjust the disconnectCause CODE to match the tone.