Revert "Revert "Allow libz to have stub even though it's not an ..."

Revert submission 1313718-revert-1312595-zlib_as_stub-BVNRLZPNBJ

Reason for revert: relanding

Reverted Changes:
I0cf486d9b:Revert "libz provides stubs to Mainline modules."
I412132f8a:Revert "libz is a stub"
I617eb90a3:Revert "Allow libz to have stub even though it's n...

Exempt-From-Owner-Approval: this is a clean relanding.

Test: m

Change-Id: Ib09a615bd11cf2647dcad42108adfcfc5040940f