[bug] inherited accessors (getters/setters) don't work.

Accessors with Buble only work without inheritance. But with inheritance, the context of an accessor is wrong (the this).

For example, in

class Foo {
  set foo(v) {console.log('set foo')}
  get foo() {return console.log('get foo')}
}

class Bar extends Foo {
  set foo(v) {super.foo = v}
  get foo() {return super.foo}
}

the Buble output will be something like

var Foo = function Foo () {};

var prototypeAccessors = { foo: {} };

prototypeAccessors.foo.set = function (v) {console.log('set foo')};
prototypeAccessors.foo.get = function () {return console.log('get foo')};

Object.defineProperties( Foo.prototype, prototypeAccessors );

var Bar = (function (Foo) {
  function Bar () {
    Foo.apply(this, arguments);
  }

  if ( Foo ) Bar.__proto__ = Foo;
  Bar.prototype = Object.create( Foo && Foo.prototype );
  Bar.prototype.constructor = Bar;

  var prototypeAccessors$1 = { foo: {} };
  // --------------- ERROR -----------------------------------------------------
  prototypeAccessors$1.foo.set = function (v) {Foo.prototype.foo = v};
  prototypeAccessors$1.foo.get = function () {return Foo.prototype.foo};

  Object.defineProperties( Bar.prototype, prototypeAccessors$1 );

  return Bar;
}(Foo));

and as you can see it will attempt to run Foo.prototype.foo = v and return Foo.prototype.foo for the extending accessors.

This obviously won't work because this inside of the parent class accessors will be Foo.prototype rather than an instance of Bar.

To fix this problem, maybe Buble can output something like this instead:

  prototypeAccessors$1.foo.set = function (v) {Object.getOwnPropertyDescriptor(Foo.prototype, 'foo').set.call(this, v)};
  prototypeAccessors$1.foo.get = function () {return Object.getOwnPropertyDescriptor(Foo.prototype, 'foo').get.call(this)};