Add support for VK_EXT_descriptor_heap

[spencer-lunarg]

From https://gitlab.khronos.org/Tracker/vk-gl-cts/-/issues/6505#note_606026

Basically CTS would like to be able to use Amber files for Descriptor Heap, which would require

1. Passing in VK_PIPELINE_CREATE_2_DESCRIPTOR_HEAP_BIT_EXT (note, there is no VK_PIPELINE_CREATE_DESCRIPTOR_HEAP_BIT_EXT, you need to use the VkPipelineCreateFlags2CreateInfo struct
2. A way to pass in VkShaderDescriptorSetAndBindingMappingInfoEXT