Rename LoaderResults to LauncherBinder.

LoaderResults implies a data object, not binding code specific to
Launcher UX containers. This CL merely renames this class and its
usages. It also adds a comment that explains why the functionality is
split into a base class and an implementing class.

Bug: 251502424
Test: Compilation worked correctly.
Change-Id: I01b5ac2f717e9b20612538d5c1e0ca947beb593f