plugin factory should support creating class instances

[sgratzl]

a common case is that the factory method is simply a class instantiation with the given arguments. This case should be simplified.

e.g. use a magic prefix for the factory like new <typename|default>

[sgratzl]

  /**
   * name of the method, which is the entry point of this plugin
   * options:
   *  * `<factorymethod>` the name of the factory method to use
   *  * `new <classname>` will create a new instance of the given class
   *  * `new` will create an instance of the default exported class of this module, same as `new default`
   * @default create
   */
  readonly factory: string;