layers: Add pNext parameter checking

layers: Add pNext parameter checking

Validate pNext based on the validextensionstructs tag from the XML
registry.  If the tag provides a list of valid structures, walk the
pNext list and check each node's sType value agains the
VkStructureType value associated with the structs from the list.
If no valid structure list is provided, ensure that pNext is NULL.

Invalid struct types produce errors similar to the following:
ERROR: [PARAMCHECK] Code 1 : vkCreateImage: pCreateInfo->pNext chain
 includes a structure with unexpected VkStructureType
 VK_STRUCTURE_TYPE_APPLICATION_INFO; Allowed structures are
 [VkInstanceCreateInfo, VkDeviceCreateInfo]

Change-Id: I2c2471a068cb304120c66cb4156331999f8548cd