resourceloader: Move expandModuleNames() to ResourceLoader.php

resourceloader: Move expandModuleNames() to ResourceLoader.php

This has always been an odd case, as indicicated by the cross-class
comment references, and the fact that its test cases are already
in ResourceLoaderTest.php, for convenience, as that's also where
the creation of 'module name strings' is done and tested.

Actually move it there instead of pretending it is there.

Change-Id: Ied9569436cc78704a5c1b75eeebb73f8631350f6