[turbofan] Introduce dedicated NumberToBoolean operator.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 33112a4568a2ede62b6f633492fe60f8e75da560..9bb0613c71dabe325c88bfe553b2fdf2b0de08b0 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -423,8 +423,8 @@ Type* Typer::Visitor::ToBoolean(Type* type, Typer* t) {
   if (type->Is(Type::Boolean())) return type;
   if (type->Is(t->falsish_)) return t->singleton_false_;
   if (type->Is(t->truish_)) return t->singleton_true_;
-  if (type->Is(Type::PlainNumber()) && (type->Max() < 0 || 0 < type->Min())) {
-    return t->singleton_true_;  // Ruled out nan, -0 and +0.
+  if (type->Is(Type::Number())) {
+    return t->operation_typer()->NumberToBoolean(type);
   }
   return Type::Boolean();
 }