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/confirmation_manager.cpp b/keystore/confirmation_manager.cpp
index d8c5378..acca304 100644
--- a/keystore/confirmation_manager.cpp
+++ b/keystore/confirmation_manager.cpp
@@ -115,6 +115,19 @@
     return Status::ok();
 }
 
+// Called by keystore main thread.
+Status ConfirmationManager::isConfirmationPromptSupported(bool* aidl_return) {
+    sp<IConfirmationUI> confirmationUI = IConfirmationUI::tryGetService();
+    if (confirmationUI == nullptr) {
+        ALOGW("Error getting confirmationUI service\n");
+        *aidl_return = false;
+        return Status::ok();
+    }
+
+    *aidl_return = true;
+    return Status::ok();
+}
+
 void ConfirmationManager::finalizeTransaction(ConfirmationResponseCode responseCode,
                                               hidl_vec<uint8_t> dataThatWasConfirmed,
                                               bool callAbortOnHal) {