[4/n] Migrate FP4/W4A8 CUTLASS kernels to torch stable ABI (#37503)

Signed-off-by: Mikayla Gawarecki <mikaylagawarecki@gmail.com>

csrc/libtorch_stable/quantization/cutlass_w4a8/w4a8_utils.cuh

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <cstddef>
+#include "cutlass/numeric_types.h"
+
+namespace vllm::cutlass_w4a8_utils {
+
+bool unified_encode_int4b(cutlass::int4b_t const* in, cutlass::int4b_t* out,
+                          size_t num_int4_elems);
+
+}  // namespace vllm::cutlass_w4a8_utils