layers: Set up UniqueObjectsOutputGenerator class
layers: Set up UniqueObjectsOutputGenerator class

Implements the Vulkan XML API registry-based generation
of the unique_objects layer's unique_objects_wrappers.h
header file.

Change-Id: Ie2456216bb10726dab792d39b0b9d85bb1ba528c

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools