Don't narrow against unions of constructor functions with instanceof (#38099)

* WIP

* Only narrows when the union is not all constructors

src/compiler/checker.ts

@@ -21800,6 +21800,12 @@ namespace ts {
                         emptyObjectType;
                 }
 
+                // We can't narrow a union based off instanceof without negated types see #31576 for more info
+                if (!assumeTrue && rightType.flags & TypeFlags.Union) {
+                    const nonConstructorTypeInUnion = find((<UnionType>rightType).types, (t) => !isConstructorType(t));
+                    if (!nonConstructorTypeInUnion) return type;
+                }
+
                 return getNarrowedType(type, targetType, assumeTrue, isTypeDerivedFrom);
             }