Document the linear-texture input investigation

- Add docs/in-place-inputs.md: reading the DLSS inputs in place does not work,
  because a hardware texture fetch on a HIP texture object over memory imported
  from vkd3d-proton returns stale data while plain loads and cuMemcpy2D are
  correct; records the measurements, the rule-outs and the reworked-fetch
  workaround that turned out not to pay for itself.
- Add tools/hip_vk_texture_stale_repro.cpp and its build script, the native
  Vulkan + HIP reproducer that rules out a general ROCm or RADV bug.

scripts/build_hip_vk_texture_stale_repro.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Builds build/hip_vk_texture_stale_repro: a native Vulkan + HIP check that a HIP texture object on
+# memory imported from Vulkan follows Vulkan's later writes (see tools/hip_vk_texture_stale_repro.cpp).
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+ROCM_ROOT="${ROCM_ROOT:-/opt/rocm}"
+mkdir -p "$ROOT/build"
+"$ROCM_ROOT/bin/hipcc" -std=c++17 -O2 "$ROOT/tools/hip_vk_texture_stale_repro.cpp" -lvulkan \
+  -o "$ROOT/build/hip_vk_texture_stale_repro"
+printf 'Built %s (run with LD_LIBRARY_PATH=%s/lib:%s/lib/llvm/lib)\n' "$ROOT/build/hip_vk_texture_stale_repro" "$ROCM_ROOT" "$ROCM_ROOT"