Add `previous_api` property to `java_api_library` module

`Previous_api` is used to migrate nullness information in metalava (i.e.
convert @Nullable and @NonNull to @RecentlyNullable and @RecentlyNonNull
for some methods). The input is required to generate loosely equivalent
from-text stubs.

Test: m && compare nullness annotations between from-source stubs and from-text stubs
Bug: 293962901
Change-Id: Ic7a0868415fdb2c65d0d472e527fe73280b7651d