Mark Settings as a "core" app.

This ensures settings is still loaded when the framework loads in a
minified state (e.g. while encrypting the device).

Bug: 5031399
Change-Id: I8c1c7331eb34c192abb18b9a77426f2e028baccb

AndroidManifest.xml

@@ -1,5 +1,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
         package="com.android.settings"
+        coreApp="true"
         android:sharedUserId="android.uid.system">
 
     <original-package android:name="com.android.settings" />