API council changes for ResourcesLoaders

Per API council guidance, setLoaders, getLoaders, and clearLoaders
are no longer part of the public API. addLoader and removeLoader
are now consume variadic loaders.

Bug: 142716192
Test: atest FrameworksResourceLoaderTests
Change-Id: If29d47b526ae6acd582b14206b2c6372f3c497be