[Kernel] Add fused grouped_topk kernel for MoE (#23274)

Signed-off-by: Xin Yang <xyangx@amazon.com>
Co-authored-by: Wentao Ye <44945378+yewentao256@users.noreply.github.com>

csrc/moe/moe_ops.h

@@ -22,6 +22,11 @@ torch::Tensor moe_wna16_gemm(torch::Tensor input, torch::Tensor output,
                              torch::Tensor num_tokens_post_pad, int64_t top_k,
                              int64_t BLOCK_SIZE_M, int64_t BLOCK_SIZE_N,
                              int64_t BLOCK_SIZE_K, int64_t bit);
+
+std::tuple<torch::Tensor, torch::Tensor> grouped_topk(
+    torch::Tensor const& scores, torch::Tensor const& scores_with_bias,
+    int64_t n_group, int64_t topk_group, int64_t topk, bool renormalize,
+    double routed_scaling_factor);
 #endif
 
 bool moe_permute_unpermute_supported();