Use module-lib system modules when building from prebuilts

When building from source the build uses the java system modules for
the public or module APIs as needed. However, previously when building
from prebuilts it would always use the public API. That difference lead
to build failures when building from prebuilts.

This change makes the selection of java system modules when building
from prebuilts consistent with the selection when building from
sources.

As API levels 30 and 31 (which are the only previous releases to
provide system modules) did not provide separate java system modules
for the module-lib API those levels always use the public APIs.

Bug: 204189791
Test: - before applying these change
      m TARGET_BUILD_APPS=framework-connectivity
      - build fails with compilation error due to missing module APIs
      m sdk dist
      cp out/dist/system-modules/module-lib/core-for-system-modules.jar prebuilts/sdk/current/module-lib/core-for-system-modules.jar
      - apply these changes
      m TARGET_BUILD_APPS=framework-connectivity
      - build passes as expected
Change-Id: Id113ff014e7892b1009fbcaad89b1ae23a7c3b79