Function isTypeAssignableTo

test/fixtures/snapshot/typescript.js:63842–63844

(source, target)

            return isTypeRelatedTo(source, target, subtypeRelation);
        }
        function isTypeAssignableTo(source, target) {
            return isTypeRelatedTo(source, target, assignableRelation);
        }
        // An object type S is considered to be derived from an object type T if
        // S is a union type and every constituent of S is derived from T,
        // T is a union type and S is derived from at least one constituent of T, or