[wasm] Fix hash value of ValueType

Since the equality operator uses the whole encoded bitfield, also the
hash value should use that. Otherwise get get unnecessary hash
collisions, resulting in bad hash table performance (e.g. in the
signature map).

R=manoskouk@chromium.org

Bug: v8:12593
Change-Id: I6f9b8ed1789ee937c90ece15d78b2bf5a3c357a6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3435189Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78921}

src/wasm/value-type.h

@@ -534,6 +534,9 @@ class ValueType {
  private:
   STATIC_ASSERT(kV8MaxWasmTypes < (1u << kHeapTypeBits));
 
+  // {hash_value} directly reads {bit_field_}.
+  friend size_t hash_value(ValueType type);
+
   using KindField = base::BitField<ValueKind, 0, kKindBits>;
   using HeapTypeField = KindField::Next<uint32_t, kHeapTypeBits>;
 
@@ -554,7 +557,8 @@ static_assert(ValueType::kLastUsedBit < 8 * sizeof(ValueType) - kSmiTagSize,
               "ValueType has space to be encoded in a Smi");
 
 inline size_t hash_value(ValueType type) {
-  return static_cast<size_t>(type.kind());
+  // Just use the whole encoded bit field, similar to {operator==}.
+  return static_cast<size_t>(type.bit_field_);
 }
 
 // Output operator, useful for DCHECKS and others.