zink: SPIR-V version fixes
This untangles the Vulkan version and SPIR-V version a bit, moves the calculation of the SPIR-V version out of the compiler, and fixes a bug where we incorrectly always exposed a cap.
With this, it should be possible to add a driconf option or a debug environment variable to override the version selection, to work around bugs in applications like renderdoc.
Edited by Erik Faye-Lund