`VK_KHR_maintenance4` extension is core in Vulkan 1.3. As Blender
should support Vulkan 1.2 we should not enable this extension when
it isn't available.
This fixes issue to run Vulkan backend on certain backends.
Maintenance4 is used to relax the interface matching rules to allow
a larger output vector to match with a smaller input vector, with
additional values being discarded.
When Maintenance4 isn't enabled a few shaders might run a bit slower
as it triggers a performance notice.
Jeroen Bakker