Make LatLngBounds obey its argument order

[tmcw]

fixes #2415

[lucaswoj]

Could you provide a little more context for this PR? What do you mean by "obey its argument order"? Can you demonstrate the behavior with a unit test?

[tmcw]

See the referenced issue #2415 for the details

[lucaswoj]

Could this code be rewritten as 👇?

setNE: function(ne) {
    if (!ne) return this;
    ne = LngLat.convert(ne) || LngLatBounds.convert(ne);
    this._ne = new LngLat(ne.lng, ne.lat);
    return this;
}

[lucaswoj]

Refactored and fixed failing unit tests.

There are some unit test "expected value" updates that raise a red flag in my head.

@mourner @morganherlocker What do yout think about these changes? How painful will this breaking change be to our users?

[mourner]

@lucaswoj not sure how many people used the reverse order for the bounds, but it's easy to upgrade at least.

[lucaswoj]

@mourner Sounds good to me. Is this ready to 🚢?