Unify object creation with empty and from_proto_and_data methods

[jedel1043]

Another step towards #577.

This Pull Request unifies JsObject creation by just having to specify an (optional) prototype and an ObjectData to create a new JsObject.

This refactors patterns like:

let obj = context.construct_object();
obj.set_prototype_instance(prototype);
obj.borrow_mut().data = ObjectData::string("".into());

into a simpler:

let obj = JsObject::from_proto_and_data(Some(prototype), ObjectData::string("".into()));

and the expression:

let obj = JsObject::new(Object::Default());

is replaced with:

let obj = JsObject::empty();

Also made the JsObject::new method private, because we only used it in the latter expression and in a few tests that can perfectly use from_proto_and_data

[github-actions]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	80,930	80,930	0
Passed	36,864	36,864	0
Ignored	12,690	12,690	0
Failed	31,376	31,376	0
Panics	0	0	0
Conformance	45.55%	45.55%	0.00%

[jedel1043]

Holding the ready for review until #1445 merges

[RageKnify]

LGTM, Razican's proposal sounds like a nice QoL improvement.

[Razican]

Looks good, just needs a rebase :)