Refactor: move getRealChildNodes and getRealChildren to core

[samouri]

summary
In order to remove Runtime dependencies from amp-layout's buildCallback, I've extracted getRealChildNodes and getRealChildren to core from CE and BE.

The primary diff in most files looks like this:

-const children = this.getRealChildren();
+const children = getRealChildren(this.element);

---

Note: I've noticed that in the transition from classic to bento, we are making lots of small tradeoffs that reduce our reliance on runtime code (v0.js) and will end up duplicated in all of the extensions. It is definitely a worthwhile tradeoff, but at some point far in the future may be worth mitigating.

[amp-owners-bot]

Hey @jridgewell! These files were changed:

src/core/dom/layout.js
src/core/dom/query.js

[rcebulko]

Looks good! Related tests should join test-query.js instead of test-dom.js, but otherwise approving to unblock

[rcebulko]

Would this change handle a basic Element less efficiently since it's not using the built-in iterator here?

[samouri]

Thats a good question! I don't know why the underlying realChildNodes isn't directly using element.childNodes, since it seems to be attempting to do the same thing. @jridgewell do you know?

[rcebulko]

It looks like this is checking whether getRealNodes is defined, ie "Is this a CustomElement? If so, use our helper to get the real children, otherwise it's an ordinary element and we should use its children because they're all "real""

[samouri]

Definitely what it is doing. My question is: "why does childNodes exist as a helper".

amphtml/src/core/dom/query.js

Lines 250 to 265 in c88b275

	/**
	* Finds all child nodes that satisfy the callback.
	* These nodes can include Text, Comment and other child nodes.
	* @param {!Node} parent
	* @param {function(!Node):boolean} callback
	* @return {!Array<!Node>}
	*/
	export function childNodes(parent, callback) {
	const nodes = [];
	for (let child = parent.firstChild; child; child = child.nextSibling) {
	if (callback(child)) {
	nodes.push(child);
	}
	}
	return nodes;
	}

Can we replace it with toArray(node.childNodes).filter(callback) Or iterate through el.childNodes directly

[samouri]

From further investigation, this is only used in two places. Will remove it entirely in a followup PR.

[rcebulko]

nit: https://github.com/ampproject/amphtml/blob/main/src/core/types/index.js#L28