DO NOT MERGE libgui: Plumb attach/detach through Surface

Exposes the attachBuffer and detachNextBuffer calls from
IGraphicBufferProducer to the public Surface interface. Also moves
the version of connect that takes a producer callback from protected
to public.

Bug: 19628705
Change-Id: I9ebc3013c4d9c84c4e8ef150c00e03f8af80319e
(cherry picked from commit c14ecb9d)