feat: Implement JSValue::new_array and other small clean up

[Hywan]

Built on top of #16.

This PR should ideally be reviewed commit-by-commit for a better experience.

Basically, it adds JSValue::new_array.
In addition, it adds JSValue::new_inner which simplify the code greatly.
Finally, it implements From<JSValue> for JSException, which adds another simplification of the code.

[waywardmonkeys]

I'm tempted to just merge this as is, but I wanted to bring up some thoughts I had about JSException since this touches some of that.

I think what you have is fine for now, but should be revisited in that area comprehensively. I think the JSException should be storing a JSObject instead which is an actual exception. There's some other accessors that need to be added.

I was looking at https://github.com/WebKit/WebKit/blob/f8937a35f02f3c64eb02529b413b65c33d65e565/Source/JavaScriptCore/API/glib/JSCException.cpp for some ideas on what things should look like in this regard.

But as I said ... I think I'll land this and then we can revisit.

What do you think?

[Hywan]

I would prefer to see this PR merged, and to open an issue to land the ideas about JSException improvements. I've other ideas about exceptions too, like result and exception must be exclusively set if I understand it well, and we should add some macros to handle and to ensure that. It can part of another PR.

[waywardmonkeys]

Sure thing. And I was out for a couple of hours (I'm GMT+5), but I'll be around to merge stuff and so on for the next 3-4 hours now.

[Hywan]

Perfect, thanks! I'm on UTC+2. Maybe we can talk in a Matrix room or a similar network?