message: refactor(interfaces): replace type aliases
  See
diff: import { Observable } from './Observable';
  -export type UnaryFunction<T, R> = (source: T) => R;
  +export interface UnaryFunction<T, R> { (source: T): R; }
  -export type OperatorFunction<T, R> = UnaryFunction<Observable<T>, Observable<R>>;
  +export interface OperatorFunction<T, R> extends UnaryFunction<Observable<T>, Observable<R>> {}
  export type FactoryOrValue<T> = T | (() => T);
  -export type MonoTypeOperatorFunction<T> = OperatorFunction<T, T>;
  +export interface MonoTypeOperatorFunction<T> extends OperatorFunction<T, T> {}
  