Make test api extend system in sdk_library.go

The test stubs for the "main" android API are being changed to
incude @SystemApi annotated APIs. Update sdk_library to make modules
and optional libraries follow the same principle.

Bug: 129133308
Test: presubmit
Exempt-From-Owner-Approval: cp
Change-Id: I7bd940e1a8127d954d30c532c74d684a5ba9d33c
Merged-In: I7bd940e1a8127d954d30c532c74d684a5ba9d33c
(cherry picked from commit 13dbaac5)
(cherry picked from commit 4fe970f3)