[turbofan] Introduce dedicated BitcastWordToTagged machine operator.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index c4c9a35724201ec5c770b7b2f3e6710210ee7d52..cd8b87ca31f3a5eb6e6e551041a52b466c6ca465 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -2217,6 +2217,9 @@ Type* Typer::Visitor::TypeUint64LessThanOrEqual(Node* node) {
 
 Type* Typer::Visitor::TypeUint64Mod(Node* node) { return Type::Internal(); }
 
+Type* Typer::Visitor::TypeBitcastWordToTagged(Node* node) {
+  return Type::TaggedPointer();
+}
 
 Type* Typer::Visitor::TypeChangeFloat32ToFloat64(Node* node) {
   return Type::Intersect(Type::Number(), Type::UntaggedFloat64(), zone());