Add test for prebuilt_apis creation of system modules

Previously, there were no tests for this (outside uses in other tests).
This change adds a test that uses the fixture preparers that create a
prebuilt_api in order to make prebuilt APIs available. That ensures
that both the prebuilt_api is working as expected and the preparer
creates a realistic test environment.

Bug: 204189791
Test: m nothing
Change-Id: I57352aa00f7b268e5286be92f177764dd63ba7e8