Create a filegroup for public stub sources

For use by framework-doc-stubs, to avoid duplicating the list of
modules there.

Bug: 169103987
Test: m framework-doc-stubs ; diff intermediates before & after
Merged-In: Ib1a1d1bb9fcf866278c6ddd057712a9c92716dbf
Change-Id: Ib1a1d1bb9fcf866278c6ddd057712a9c92716dbf
2 files changed