libbase: add libbase_headers

Test: can include headers in other soong modules
Bug: 33241851
(cherry picked from commit 8f56c1ecd71dc142b3fd02826ba4e8b37485c1d0)
Merged-In: Ie3d11d1559f5aae46125695fd1f3a63da8e429ae
Change-Id: Ie3d11d1559f5aae46125695fd1f3a63da8e429ae
1 file changed