loader: Add additional extensions to ext emulation
loader: Add additional extensions to ext emulation

The loader will now handle structures from VK_KHX_multiview and
VK_KHX_external_memory_capabilities in the pNext fields of commands
from VK_KHR_get_physical_device_properties2.

Change-Id: Ic7175e9334c56c7642b75360b35a6b9ff240ee98

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers