Clean up some code quality issues

This removes some qualifiers that aren't necessary (e.g. public/abstract on interfaces, private on enum constructors, final on private methods, static on nested interfaces/enums), uses Java 8 lambdas and features where that's an improvement

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177182945

java/google/registry/model/common/Cursor.java

@@ -83,7 +83,7 @@ public class Cursor extends ImmutableObject {
     /** See the definition of scope on {@link #getScopeClass}. */
     private final Class<? extends ImmutableObject> scope;
 
-    private CursorType(Class<? extends ImmutableObject> scope) {
+    CursorType(Class<? extends ImmutableObject> scope) {
       this.scope = scope;
     }