Support for VK_EXT_descriptor_heap

## Description of Feature

As almost everyone knows, this [new extension](https://github.com/KhronosGroup/Vulkan-Docs/blob/main/proposals/VK_EXT_descriptor_heap.adoc) brings a variant of DX12 descriptor heaps to VK. I would need support in RenderDoc to start using it as a mainline feature.

## Environment

* RenderDoc version: 1.42
* Operating System: Windows
* Graphics API: Vulkan