Define previous_api in full api surface stubs java_api_library defaults

previous_api input is required to migrate nullness information in
metalava and generate loosely equivalent from-text stubs. Since
"android.api.public.latest" is the only input for previous_api in the
tree, this is hardcoded for full api surface java_api_library modules
defaults for now.

Test: m && compare nullness annotations for from-text stubs and from-source stubs
Bug: 293962901
Change-Id: Ic07db8c3bd37fa41ff245952c94b5c5b4773af36