Enable VK_KHR_vulkan_memory_model

[kvark]

Is your feature request related to a problem? Please describe. A pass-through of SPIR-V shaders with Vulkan memory model triggers validation.

Describe the solution you'd like WebGPU is adopting the memory model similar to Vulkan. Therefore, Vulkan backend should try to enable this extension (unless its on Vulkan 1.2), unconditionally.

Describe alternatives you've considered Exposing this as an optional feature.

Additional context Add any other context or screenshots about the feature request here.

[teoxoy]

Spec PR https://github.com/gpuweb/gpuweb/pull/2055 (related: https://github.com/gpuweb/gpuweb/issues/1621)

[jimblandy]

If I understand correctly, the extension describes behavior that drivers already provide, and the extension just describes and formalizes it. So:

• If the extension is available, we should request it.
• If the extension is not available, we should assume the device behaves that way anyway.