layer: Add utility template for sType init
layer: Add utility template for sType init

Add utility function to auto populate sType field based on typename
given to autogen of typemap helper. Return value optimization (copy
elision) should make this perfomance neutral vs. inline init.

Change-Id: I231cf92d5063c19f9ad5b14189dd162fdac76a43

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