Migrate ICaptivePortal to stable AIDL

Also add required API for the captive portal app to stop using hidden
members.

Test: atest FrameworksNetTests NetworkStackTests
Bug: 112869080
Change-Id: I62b457e709fa199822bb8f80b0eab990be4ded93

core/java/android/net/CaptivePortal.java

@@ -45,6 +45,8 @@ public class CaptivePortal implements Parcelable {
     private final IBinder mBinder;
 
     /** @hide */
+    @SystemApi
+    @TestApi
     public CaptivePortal(IBinder binder) {
         mBinder = binder;
     }
@@ -107,6 +109,8 @@ public class CaptivePortal implements Parcelable {
      * connectivity for apps because the captive portal is still in place.
      * @hide
      */
+    @SystemApi
+    @TestApi
     public void useNetwork() {
         try {
             ICaptivePortal.Stub.asInterface(mBinder).appResponse(APP_RETURN_WANTED_AS_IS);