[Call] Usage of "this" in methods is not supported

[croraf]

Describe the bug

const foo = {
  a: 3,
  bar: function () {return this.a + 5}
};

foo.bar()

should return 8. Instead thread 'main' panicked at 'Reference Error: Unitialised binding for this function', boa/src/environment/function_environment_record.rs:115:17 happens

[jasonwilliams]

Looks like the binding status is defauting to uninitialized, changing to initialized will work https://github.com/boa-dev/boa/blob/master/boa/src/builtins/function/mod.rs#L196 but we probably want to pass that value in, as we don't know at that point whether we're in an arrow function or not

[jasonwilliams]

There's a fix for this in #526