Add getprop to toolbox

Add a non-toybox version of getprop, so that we can interface with the
new C++ PropertyInfoAreaFile class to return property context
information.

Bug: 36001741
Test: Compared toolbox getprop results with toybox getprop
Change-Id: I5f98f9e895d0620a2d9686bc0608490e7d9c3120