Use binder-based iterator to retrieve FRROs

If for some reason there are a lot of fabricated overlays in the
resources cache, the binder limit of the list of fabricated overlay
infos could exceed the maximum binder transaction size. Rather than
return all of the frro infos in one transactions, register an iterator
with the native idmap2d service and use multiple binder transactions
to iterate through all of the frros.

Bug: 192948522
Test: Toggle device theme colors several times and observe frro cache
      Reboot device and observe old frros are deleted
Change-Id: I5e9cf3ae9d1d45eda683c24141a0cd4e4301e02f