[DX] Add ray tracing state object, SBT, and DispatchRays bring-up

[MarijnS95]

Depends on #1273

Summary

Second per-backend bring-up in the PSO raytracing series (#1268). Stacks on top of #1273 (the Vulkan bring-up + the API surface). Mirrors that PR for D3D12: builds an ID3D12StateObject from the YAML schema, hands out shader identifiers via ID3D12StateObjectProperties, lays out the SBT in an upload heap, and routes DispatchRays through ID3D12GraphicsCommandList4 (same query path the AS-build already uses).

D3D12 implementation:

• DXRayTracingPipelineState derives from DXPipelineState with an IsRayTracing flag on the base for classof — matching the VulkanPipelineState pattern. It carries the ID3D12StateObject, a cached ID3D12StateObjectProperties, and a StringMap<const void *> resolving each raygen / miss / callable shader's EntryPoint and each hit-group's Name to its 32-byte shader identifier blob. The identifiers are driver-owned and stay alive for the Properties COM lifetime, so the PSO keeps Properties alive. Closest-hit / any-hit / intersection shaders are not directly addressable via GetShaderIdentifier — they're imported through a hit-group subobject — so the eager-cache loop skips them.
• DXShaderBindingTable holds a single upload-heap buffer plus four pre-built D3D12_DISPATCH_RAYS_DESC ranges (raygen, miss, hit-group, callable) — RANGE for raygen since it's always one record, and RANGE_AND_STRIDE for the others.
• createPipelineRT builds a CD3DX12_STATE_OBJECT_DESC with subobjects for the DXIL library (one export per Shader entry), per-hit-group subobjects with closest-hit / any-hit / intersection imports, the pipeline shader config (max payload + max attribute bytes), pipeline config (max recursion depth), and a global root signature subobject. The root signature comes from the library's embedded RTS0 part when present, falling back to the BindingsDesc path (matching the existing compute / raster pipeline behaviour). Wide strings for the subobject exports live in a SmallVector that outlives the SODesc, since the helper classes store pointers into the strings rather than copying.
• createShaderBindingTable lays out each entry as [identifier][LocalRootData][padding-to-stride] with per-region stride = align(D3D12_SHADER_IDENTIFIER_SIZE_IN_BYTES + max-LocalRootData-in-region, D3D12_RAYTRACING_SHADER_RECORD_BYTE_ALIGNMENT) and per-region size = align(count * stride, D3D12_RAYTRACING_SHADER_TABLE_BYTE_ALIGNMENT). The buffer lives in an upload heap with D3D12_RESOURCE_STATE_GENERIC_READ — PR3 simplification; a staging copy into a default heap is a follow-up.
• dispatchRays queries the underlying CommandListX for ID3D12GraphicsCommandList4 (matching the AS-build path), binds the global root signature via SetComputeRootSignature, calls SetPipelineState1 with the state object, and issues DispatchRays with a D3D12_DISPATCH_RAYS_DESC populated from the SBT's four ranges plus the dispatch dimensions. The descriptor heap + descriptor-table bindings are set up by the existing createComputeCommands helper before the encoder is created.
• createComputeCommands grows an isRayTracing branch at the dispatch point so it calls dispatchRays instead of dispatch, reusing all of the descriptor-heap and root-signature wiring. InvocationState carries a ShaderBindingTable unique_ptr that's only populated for RT pipelines.
• executeProgram's isRayTracing branch builds a RayTracingPipelineCreateDesc from Pipeline.Shaders / HitGroups / RTConfig, calls createPipelineRT then createShaderBindingTable, then re-enters createComputeCommands which dispatches via the new RT path.

Test side: raygen-roundtrip.test's XFAIL becomes Clang, Metal — DirectX should PASS via this implementation on Windows CI (and via Wine + vkd3d-proton locally on Linux). The Clang token still catches the compile failure on clang-dxc since [shader("raygeneration")] doesn't yet lower to either DXIL libraries or SPIR-V on that path.

Test plan

• End-to-end run on Wine + vkd3d-proton against an NVIDIA RTX 3060: compiled the foundational test's library with wine dxc.exe -T lib_6_5 and ran wine offloader.exe pipeline.yaml lib.o lib.o lib.o. Output buffer = [ 48879 ] (0xBEEF) — TraceRay hit the triangle, the closest-hit shader ran, the payload round-tripped to raygen, raygen wrote the sentinel to the UAV. vkd3d-proton logs confirm DXR 1.1 enabled and the state object created without complaints.
• Windows CI: same raygen-roundtrip.test should PASS on DXC + native D3D12 hardware.
• No-RT-support code paths (DX device with RaytracingTier == NotSupported): the test should be UNSUPPORTED via the REQUIRES: raytracing-pipeline gate, not run.
• Vulkan unchanged from [VK] Add ray tracing pipeline, SBT, and DispatchRays bring-up #1273 (test still PASSes on DXC + Vulkan), Metal still XFAILs.