[Call Screening]Default call screening app setting storage.

Add new string in Settings. To indicate which app is default
call screening, similar to default dialer application setting,
store this in the system settings provider.

Bug: 118416082
Test: atest SettingsBackupTest pass.
Change-Id: I39f81b31a68ee2dbb056ff935f8dea0f51720017
diff --git a/core/tests/coretests/src/android/provider/SettingsBackupTest.java b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
index e62dbea..d498268 100644
--- a/core/tests/coretests/src/android/provider/SettingsBackupTest.java
+++ b/core/tests/coretests/src/android/provider/SettingsBackupTest.java
@@ -530,6 +530,7 @@
                  Settings.Secure.BACKUP_PROVISIONED,
                  Settings.Secure.BACKUP_TRANSPORT,
                  Settings.Secure.CALL_REDIRECTION_DEFAULT_APPLICATION,
+                 Settings.Secure.CALL_SCREENING_DEFAULT_COMPONENT,
                  Settings.Secure.CAMERA_LIFT_TRIGGER_ENABLED, // Candidate for backup?
                  Settings.Secure.CARRIER_APPS_HANDLED,
                  Settings.Secure.CMAS_ADDITIONAL_BROADCAST_PKG,