vulkan: add pNext chain boilerplate for physical device features

We now "officially" support enabling arbitrary extra device features,
including both features request by the user and features needed by us.

It's about time for me to write the shitty boilerplate to link and
memdup chains and stuff. Using generated code to get the sizeof()
unknown structs, because how the heck else would you copy over a pNext
chain while only modifying the values you care about?

Still using shitty hacks for the features whitelisting. I hope they
never change the structure of these arrays as just being a list of
VkBool32 values. (But in theory we could just generate code for this, in
the worst case....)