libui: Load a.h.graphics.mapper passthrough service on library load

Zygote loads libui, this helps complete the chain from
  zygote -> libui -> a.h.graphics.mapper -> gralloc
so that all of these libraries which are used by nearly every app are
loaded by zygote and shared.

Bug: 62353585
Test: boot to launcher, run calculator, confirm a.h.graphics.mapper
      implementation library is in /proc/`pid zygote64`/maps

Change-Id: Ib505c926a410191e3e2ad809bfe98a73b21fac90