Replace ctx.ExpandSources with android.PathsForModuleSrc

Move the logic from ctx.ExpandSources into android.PathsForModuleSrc
and ctx.ExpandSource into android.PathForModuleSrc, and deprecate
them.  When combined with the pathDepsMutator this will let all
properties that take source paths also take filegroups or genrule
outputs, as long as they are tagged with `android:"path"`.

Test: All soong tests
Change-Id: I01625e76b5da19240e9649bf26a014eeeafcab8f