layers: Update vulkan.py for new extension APIs
layers: Update vulkan.py for new extension APIs

Added extension protos and update extension lists for
VK_AMD_draw_indirect_count, VK_NV_external_memory_capabilities,
and VK_NV_external_memory_win32 new for header version 1.0.25.

Change-Id: Ifac0a2b4b7e36a8f907622e002ec419cc7c54f87

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