Revert "Revert "Make CtsShim*Prebuilt be available to the test APEXes""

This reverts commit 77cd43a7.

We need a cts shim apex target with prebuilts so that GSI can install
cts shim apks as a part of flattened cts shim apex.

Bug: 159392784
Test: lunch aosp_arm64-userdebug
      m droid => should have cts shim in /system/system_ext/apex/
Change-Id: Ib18dd105d7b959774654182783b973b732127986