[turbofan] Introduce dedicated BitcastWordToTagged machine operator.

src/compiler/raw-machine-assembler.h

Index: src/compiler/raw-machine-assembler.h
diff --git a/src/compiler/raw-machine-assembler.h b/src/compiler/raw-machine-assembler.h
index 735fff40660854b11a9d47d7a81e2eb5faffa7b7..eeddbb94568a94a0a4f1363a1f6fc83b31e348e1 100644
--- a/src/compiler/raw-machine-assembler.h
+++ b/src/compiler/raw-machine-assembler.h
@@ -469,6 +469,9 @@ class RawMachineAssembler {
   }
 
   // Conversions.
+  Node* BitcastWordToTagged(Node* a) {
+    return AddNode(machine()->BitcastWordToTagged(), a);
+  }
   Node* ChangeFloat32ToFloat64(Node* a) {
     return AddNode(machine()->ChangeFloat32ToFloat64(), a);
   }