vulkan: Implement topk_moe fused shader, ported from CUDA (llama/16641)

This is similar to the CUDA shader from #16130, but doesn't use shared memory
and handles different subgroup sizes.

ggml/src/ggml-impl.h

@@ -565,14 +565,23 @@ static inline ggml_bf16_t ggml_compute_fp32_to_bf16(float s) {
 #define GGML_FP32_TO_BF16(x) ggml_compute_fp32_to_bf16(x)
 #define GGML_BF16_TO_FP32(x) ggml_compute_bf16_to_fp32(x)
 
+static inline int32_t ggml_node_get_use_count(const struct ggml_cgraph * cgraph, int node_idx) {
+    const struct ggml_tensor * node = cgraph->nodes[node_idx];
+
+    size_t hash_pos = ggml_hash_find(&cgraph->visited_hash_set, node);
+    if (!ggml_bitset_get(cgraph->visited_hash_set.used, hash_pos)) {
+        return 0;
+    }
+    return cgraph->use_counts[hash_pos];
+}
+
 // return true if the node's results are only used by N other nodes
 // and can be fused into their calculations.
 static inline bool ggml_node_has_n_uses(const struct ggml_cgraph * cgraph, int node_idx, int32_t n_uses) {
     const struct ggml_tensor * node = cgraph->nodes[node_idx];
 
     // check the use count against how many we're replacing
-    size_t hash_pos = ggml_hash_find(&cgraph->visited_hash_set, node);
-    if (!ggml_bitset_get(cgraph->visited_hash_set.used, hash_pos) || cgraph->use_counts[hash_pos] != n_uses) {
+    if (ggml_node_get_use_count(cgraph, node_idx) != n_uses) {
         return false;
     }