[ET-VK] Plumb subgroup property queries + VK_EXT_subgroup_size_control

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [ET-VK] Plumb subgroup property queries + VK_EXT_subgroup_size_control #19403
• [ET-VK] Make libtorch optional in custom op test binaries #19402

Adds infrastructure for querying GPU subgroup capabilities and pinning required subgroup size at pipeline creation time, sourced from the existing SUBGROUP_SIZE yaml template parameter. This is the foundation for writing subgroup-using shaders (e.g. cooperative GEMV variants) that remain portable across GPUs with different subgroup widths (Adreno=64, Mali=16, NVIDIA=32, etc.).

PhysicalDevice now chains VkPhysicalDeviceSubgroupProperties and VkPhysicalDeviceSubgroupSizeControlProperties into vkGetPhysicalDeviceProperties2, plus VkPhysicalDeviceSubgroupSizeControlFeatures into vkGetPhysicalDeviceFeatures2. The Adapter exposes accessors for subgroup_size, supported subgroup ops/stages, [min,max] subgroup size range, and whether the driver supports per-pipeline required subgroup size for the COMPUTE stage. VK_EXT_subgroup_size_control is added to the requested extension list and the size-control features are chained into device-create pNext when supported.

ComputePipeline::Descriptor gains a required_subgroup_size field that, when nonzero, chains VkPipelineShaderStageRequiredSubgroupSizeCreateInfoEXT into pipeline creation (both the on-demand retrieve path and the batch create_pipelines path). The pipeline cache key includes the field so pipelines compiled for different subgroup widths cache independently. ShaderInfo carries the same field so it can be plumbed from shader yaml through to the pipeline descriptor.

The existing SUBGROUP_SIZE yaml template parameter is now the single source of truth: gen_vulkan_spv.py substitutes it into GLSL as before AND emits it as ShaderInfo::required_subgroup_size. At dispatch, vkapi::resolve_required_subgroup_size validates the value is within the adapter's [min, max] range and throws ShaderNotSupportedError if the extension is unsupported or the value is out of range, surfacing a clear failure rather than silently miscompiling a shader whose algorithm depends on the pinned subgroup width.

No shader yamls are modified by this change; subsequent commits opt their shaders into the pinning by declaring SUBGROUP_SIZE in their yamls.

Differential Revision: D104456803

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