zink: should a minimum vulkan version be required?

For many years, the claim has been that zink can work on vulkan 1.0. This is a claim which has been disproved many times over the years, and it isn't tested either.

Given that 1.3 came out over 2 years ago, I'm proposing that before the next version of mesa, zink should begin requiring vulkan 1.2 (2020). This would allow deleting/simplifying a lot of code, and realistically I don't care about any tickets coming in from people using 1.0 these days, so it's win/win.

If I don't hear any strong arguments for keeping questionable 1.0 support in a few weeks, I'll begin implementing requirements.