Remove String, Number, and Boolean from TypeFlags.Falsy

Author: ahejlsberg

src/compiler/types.ts

@@ -2224,7 +2224,8 @@ namespace ts {
 
         /* @internal */
         Nullable = Undefined | Null,
-        Falsy = String | Number | Boolean | Void | Undefined | Null,
+        /* @internal */
+        Falsy = Void | Undefined | Null,       // TODO: Add false, 0, and ""
         /* @internal */
         Intrinsic = Any | String | Number | Boolean | ESSymbol | Void | Undefined | Null | Never,
         /* @internal */