Define core-current-stubs-for-system-modules-exportable

This module is an "exportable" version of
core-current-stubs-for-system-modules, which is built as an artifact for
sdk builds.

Test: m sdk dist && inspect ninja graph
Bug: 359561906
Change-Id: I16f21f9aeba6d16f3fea77b1fc2a591b1ded281a