Add AppSettings page

Including the following features,
- App icon
- App label
- Display over other apps item
- Modify system settings item
- Picture in picture item
- Install unknown apps item
- App version

Bug: 236346018
Test: Manual with Settings App
Change-Id: Ieabdd32fac1d0992ba5c22d459631b42a17ce32a

src/com/android/settings/applications/manageapplications/ManageApplications.java

@@ -283,7 +283,7 @@ public class ManageApplications extends InstrumentedFragment
         final String className = getClassName(activity.getIntent(), getArguments());
         if (className.equals(ManageExternalSourcesActivity.class.getName())) {
             SpaActivity.startSpaActivity(
-                    context, InstallUnknownAppsListProvider.INSTANCE.getRoute());
+                    context, InstallUnknownAppsListProvider.INSTANCE.getAppListRoute());
             activity.finish();
         }
     }