Pass shared library updatability attributes as strings

Migrate from ints to Strings so we can pass codenames. Otherwise we
can't use these attributes representing a release in progress until that
release is finalized. I.e. if release T is in progress, we don't get the
correct behaviour if we use "T" in those attributes

Bug: 191978330

Test: m nothing
Change-Id: I35389da0a01549ba2f820f5e5b78f6ea88c2aea1