Add isConfirmationPromptSupported() method.

This will be used by the android.security.ConfirmationDialog.isSupported() and
is intended so that apps can know ahead of time whether the device implements
the ConfirmationUI HAL.

Bug: 63928580
Test: Manually tested.
Change-Id: I6347824b4e2330a93b7a7ffd7cf5b206009a564e
diff --git a/keystore/key_store_service.h b/keystore/key_store_service.h
index ce809f8..70a56ca 100644
--- a/keystore/key_store_service.h
+++ b/keystore/key_store_service.h
@@ -175,6 +175,7 @@
     ::android::binder::Status
     cancelConfirmationPrompt(const ::android::sp<::android::IBinder>& listener,
                              int32_t* _aidl_return) override;
+    ::android::binder::Status isConfirmationPromptSupported(bool* _aidl_return) override;
 
   private:
     static const int32_t UID_SELF = -1;