Allow using loaders on non-RM Resources instances

Currently there is a limitation where ResourcesLoaders cannot be  used
on Resources object not created through ResourcesManager. This change
creates an update handler for Resources objects that are not registered
with ResourcesManager.

The handler changes the loaders on the asset manager owned by the
Resources instance.

Bug: 151666644
Test: atest ResourceLoaderValuesTest
Change-Id: I5a89f686386bdb088dc964014e7becc0c2b4770f