provide a renderlist generated from the SurfaceStack.
This is not the final version of the interface. It is a first step towards that goal, as well as being the first step to integrating hardware optimization support down to the DisplayBuffer/HWC.
This implements a pretty shallow copy of the list. I suspect the optimal answer to 'how deep to copy' lies somewhere between a shallow copy and a deep copy, and will be hashed out in the future.
Approved by Daniel van Vugt, PS Jenkins bot, Alberto Aguirre.