scripts: Add pNext-chain extension helper function
scripts: Add pNext-chain extension helper function

Unique-objects layer did not handle extension structs or chains of
extension structs. Automated generation and handling of unwrapped
struct chains.

Change-Id: I8cc813c9bf7290bbcec257245848e54e1ce8a0f7

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