Add filename property to prebuilt_apex

* Makes it more inline with prebuilt_etc;
* For shim apexes, prebuilt_apex modules have pattern of
  com.android.apex.cts.shim.v1_prebuilt, but I would prefer
  pre-installed shim to be: /system/apex/com.android.apex.cts.shim.apex

Bug: 128677967
Bug: 127789981
Test: m
Change-Id: I34e3e078733420b5cf777fd6e3ce4d8c5796b19b