[VK] Add ray tracing pipeline, SBT, and DispatchRays bring-up

[MarijnS95]

Depends on #1270

Summary

First per-backend bring-up in the PSO raytracing series (#1268). Stacks on top of #1270 (foundational schema + lit infrastructure + XFAILed test). Adds the API surface needed by the upcoming D3D12 and Metal PRs plus the Vulkan implementation behind it.

API surface:

• ComputeEncoder::dispatchRays(PSO, SBT, W, H, D) virtual on the existing compute encoder (no separate RayTracingEncoder).
• Device::createPipelineRT + Device::createShaderBindingTable virtuals with a new RayTracingPipelineCreateDesc carrying the DXIL library blob, the shader entry points (Stage + EntryPoint), the hit-group list, and the RayTracingPipelineConfig.
• include/API/ShaderBindingTable.h holding the abstract runtime base; backend SBT classes derive from it with LLVM-style classof / cast<>.
• Rename: PR Add RayTracing pipeline kind, shader stages, and YAML schema #1270's YAML struct ShaderBindingTable → ShaderBindingTableDesc so the bare name is free for the runtime class (parallel to BLASDesc / TLASDesc vs AccelerationStructure). YAML key stays ShaderBindingTable:.
• D3D12 and Metal stub the new methods with not-yet-supported errors; their bring-up lands in follow-up PRs.

Vulkan implementation:

• The pre-existing RaytracingFunctions RT struct lumped AS and RT-pipeline entry points together; they split into ASFunctions AS + RTPipelineFunctions RT so the names match the actual feature-gate split (AS + ray-query is a complete configuration; RT pipeline layers on top). HasRayTracingSupport renames to HasASSupport; HasRTPipelineSupport tracks the new extension.
• VK_KHR_ray_tracing_pipeline is requested when reported, with VkPhysicalDeviceRayTracingPipelineFeaturesKHR chained pre-query and the gating rayTracingPipeline bool checked post-query (matches the AS / BDA pattern from Add RT acceleration structure abstraction with size queries and resource allocation #1232). Sub-features the tests don't exercise (capture-replay / indirect-trace / traversal-primitive-culling) are cleared.
• Function pointers vkCreateRayTracingPipelinesKHR, vkGetRayTracingShaderGroupHandlesKHR, vkCmdTraceRaysKHR resolve once at device creation. VkPhysicalDeviceRayTracingPipelinePropertiesKHR is cached at the same time for SBT handle size / alignment / base alignment.
• VKRayTracingPipelineState derives from VulkanPipelineState; an IsRayTracing flag on the base lets the existing Vulkan cast<> path stay polymorphic without adding a new GPUAPI value. The derived class also carries a StringMap<uint32_t> resolving each shader EntryPoint or hit-group Name to its index in the pipeline's group array, plus per-bucket counts so the SBT builder can slice the contiguous handle blob into raygen / miss / hit / callable regions.
• createPipelineRT builds a single VkShaderModule (the DXIL library compiles to one SPIR-V module with multiple OpEntryPoints), one VkPipelineShaderStageCreateInfo per Shader entry, and one VkRayTracingShaderGroupCreateInfoKHR per general shader / hit group. Pipeline layout uses the same createPipelineLayout helper as the compute path, gated on all six RT stage flags so any binding can be consumed from any RT shader.
• createShaderBindingTable allocates a host-visible coherent buffer big enough for four regions, then lays out each entry as [handle bytes][LocalRootData bytes][padding-to-stride]. Per-region stride = align(handleSize + max-LocalRootData-in-region, handleAlignment); per-region size = align(count * stride, baseAlignment). LocalRootData support comes for free from PR Add RayTracing pipeline kind, shader stages, and YAML schema #1270's SBT schema; the test doesn't exercise it yet. Each region's VkStridedDeviceAddressRegionKHR derives from the buffer's vkGetBufferDeviceAddress.
• dispatchRays binds the pipeline at VK_PIPELINE_BIND_POINT_RAY_TRACING_KHR, emits a pre-barrier with ACCELERATION_STRUCTURE_READ_BIT_KHR | SHADER_READ_BIT | SHADER_WRITE_BIT dst access into RAY_TRACING_SHADER_BIT_KHR, then calls vkCmdTraceRaysKHR with the SBT's four region structs.
• createCommands picks the new bind point for RT pipelines so vkCmdBindDescriptorSets binds to the right point. executeProgram's isRayTracing branch builds a RayTracingPipelineCreateDesc from the Pipeline, calls createPipelineRT then createShaderBindingTable, and keeps both on InvocationState for the dispatch.

Test side: raygen-roundtrip.test's XFAIL becomes Clang, DirectX, Metal. On a DXC + Vulkan combo with the device reporting VK_KHR_ray_tracing_pipeline this should PASS; the Clang token still catches the compile failure on the Linux + clang-dxc loop where [shader("raygeneration")] doesn't yet lower to SPIR-V.

Test plan

• Full build clean.
• clang-vk lit suite unchanged: 306 PASS, 144 XFAIL, 4 pre-existing FAIL, 1 pre-existing XPASS.
• Feature/RT/raygen-roundtrip.test still XFAILs on Clang as expected.
• CI on a DXC + Vulkan setup: raygen-roundtrip.test should PASS now. The local Linux + Clang loop can't verify this because clang-dxc doesn't lower RT entry points to SPIR-V yet, and Arch's dxc 1.8 asserts on lib_6_5. RenderDoc should show vkCmdTraceRaysKHR called with four VkStridedDeviceAddressRegionKHR regions covering raygen / miss / hit / (empty) callable.
• No-RT-support code paths (Vulkan device without VK_KHR_ray_tracing_pipeline): the test should be UNSUPPORTED via the REQUIRES: raytracing-pipeline gate, not run.