fix: call getter accumulator with proper this context

[Julien-R44]

Proposed changes

Without this fix, then the following code did not work:

class Foo extends Macroable {
  public value = "foo";
}

Foo.getter("bar", function (this: Foo) {
  console.log(this); // print undefined
  return this.value;
});

const foo = new Foo();
console.log(foo.bar);

In other words: the this context was not passed to the getters callback. I added a test in the PR that showed this behavior.
This also caused an undesired breaking change

[thetutlage]

Thanks 👍