In their current implementation, both the NodeIterator and TreeWalker would
skip over ignored nodes. However, while the node itself should have been ignored
its children should still be iterated.
For example, when going over:
```
<div id="container">
<!-- comment1 -->
<span>
<!-- comment2 -->
</span>
</div>
```
With `SHOW_COMMENT`, the previous version would completely skip over `container`
and its children. Now the code still won't emit the `container` div itself,
it will still iterate through its children (and thus emit the two comments).
This change relates to ongoing react compatibility.
1 - Always fire the callback on the next tick. This is probably the most
important change, as frameworks like React don't react well if the callback is
fired immediately (they expect to continue processing the page in its current
state, not in the mutated state from the callback)
2 - Always fire the callback for observed elements with a parent, whether or
not those intersect or are connected. From MDN, the callback is fired
"The first time the observer is initially asked to watch a target element."
3 - Add a mutation observer so that if a node is added to the root (or removed)
the callback is fired. This, I think, is the best we can currently do for
"intersection".
Renames JsContext -> js.Context, JsObject -> js.Object and JsThis -> js.This
which is more consistent with the other types. The JsObject -> js.Object is
the reason so many files were touched.
This is still a [messy] transition, with more refactoring planned to clean it
up.
scroll alias for scrollTo
add get_scrollX and get_scrollY, along with their aliases: pageXOffset and
pageYOffset. These always return 0, unless scroll or scrollTo are called.
There's always going to be ambiguity between a string and a Uint8Array. We
already had TypedArray(u8) as a discriminator when _returning_ values. But now
the type is also used by mapping JS values to Zig. To support this efficiently
when probing the union, the typed array mapping logic was extracted into its
own function (so that it can be used by the probe).
