* [Vulkan] Add v2 of context negotiation interface.
* [Vulkan] Add vkEnumerateInstanceVersion symbol.
* [Vulkan] Implement v2 context negotiation
* [libretro] Add GET_HW_CONTEXT_NEGOTIATION_INTERFACE_SUPPORT.
Works around issues in v1 interface where it was not possible to
query what frontend would do when faces with newer interface versions.
This env-call gives stronger guarantees how things have to work.
* [runloop] Implement GET_HW_CONTEXT_NEGOATION_INTERFACE_SUPPORT.
Fairly trivial. Just report the latest version.
* [Vulkan] Add stricted wording around get_application_info in v2.
* [Vulkan] Be more defensive about get_application_info() in v1.