Add safe struct for VkPushDescriptorSetWithTemplateInfoKHR

[mikes-lunarg]

VkPushDescriptorSetWithTemplateInfoKHR is part of VK_KHR_maintenance6 which appeared in the 1.1.274 header.

Currently stubbed out so we can build, but it needs a custom constructor which can copy pData correctly.

(Codegen assumed there was a dataCount member to get the length of pData and it failed to compile)

[spencer-lunarg]

Moved issued to VUL as Safe Struct now lives here