vulkan: Implement bindless texture rendering

vulkan: Implement bindless texture rendering

Instead of having a descriptor set per operation, we just have one
descriptor set and bind all our images into it.

Then the shaders get to use an index into the large texture array
instead.

Getting this to work - because it's a Vulkan extension that needs to be
manually enabled, even though it's officially part of Vulkan 1.2 - is
insane.