dzn: Collection of fixes, cleanups and cosmetic changes
Most of those fixes were found while working on KHR_maintenance{1,2}. I ended dropping the patch advertizing KHR_maintenance1 though (I'll make it part of separate MR). Also dropped the revert adding the cpp_std=c++latest override, since this is being addressed in !15706 (merged).
/cc @jekstrand for vulkan/util: Make STACK_ARRAY() C++-friendly