Use new libcore filegroup variable

This change switches frameworks/base/ targets to a generic "interface"
libcore filegroup variable, core_public_api_files, rather than having
it know about Core Library internal filegroups. It is not perfect
because the command line tools need to know to exclude certain packages,
but it is a step in the right direction.

Bug: 126332291
Test: build only
Merged-In: I72667f30dc5685fdc24aca3f8ee82b20c7548449
Change-Id: I72667f30dc5685fdc24aca3f8ee82b20c7548449