Implement policy transparency for CredMan

This CL implements policy transparency for
Credential Manager settings.

Screenshots:
https://hsv.googleplex.com/5502938857340928
https://hsv.googleplex.com/4999933426925568

Test: on device w/ test dpc
Bug: 318552220
Change-Id: I78e1fa47541c81e6e2d2bf2c13159be01928e77c

src/com/android/settings/applications/credentials/DefaultCombinedPreferenceController.java

@@ -111,7 +111,7 @@ public class DefaultCombinedPreferenceController extends DefaultAppPreferenceCon
             @Nullable CharSequence appName,
             @Nullable String appSubtitle,
             @Nullable Drawable appIcon,
-            @Nullable CharSequence packageName,
+            @Nullable String packageName,
             @Nullable CharSequence settingsActivity) {
         if (appName == null) {
             preference.setTitle(R.string.credman_app_list_preference_none);