filter out hidden elements when copying code

[schultek]

Fixes #13253

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[gemini-code-assist]

Code Review

This pull request replaces regex-based text filtering in the CopyButton component with a DOM-based approach that removes elements marked as hidden. Review feedback identifies a potential compilation error where the remove method is called on a generic Node type and suggests optimizing the node iterator to target elements specifically. It also notes that the newly added js_interop import would become redundant if these suggestions are adopted.

[gemini-code-assist]

The current implementation contains a bug and can be optimized:

1. Bug: currentNode.remove() is called on a variable of type web.Node?. In package:web (which universal_web wraps), the remove() method is defined on the ChildNode interface (implemented by Element and CharacterData), but not on the base Node class. This will likely cause a compilation error.
2. Optimization: By default, createNodeIterator visits all nodes, including text nodes. Since you only need to check attributes on elements, using web.NodeFilter.SHOW_ELEMENT is more efficient.
3. Type Safety: Using a direct cast (safe when using SHOW_ELEMENT) or the Dart is operator for type promotion is cleaner than repeated isA checks.

Suggested change

	final iterator = web.document.createNodeIterator(codeElement);
	web.Node? currentNode;
	while ((currentNode = iterator.nextNode()) != null) {
	if (currentNode.isA<web.Element>() &&
	(currentNode as web.Element).getAttribute('aria-hidden') ==
	'true') {
	currentNode.remove();
	}
	}
	// Filter out hidden elements like the terminal sign or folding icons.
	final iterator = web.document.createNodeIterator(
	codeElement,
	web.NodeFilter.SHOW_ELEMENT,
	);
	web.Node? currentNode;
	while ((currentNode = iterator.nextNode()) != null) {
	final element = currentNode as web.Element;
	if (element.getAttribute('aria-hidden') == 'true') {
	element.remove();
	}
	}

[gemini-code-assist]

This import is only used for the isA extension method. If you apply the suggested fix for the iteration logic below (which uses a direct cast or the is operator), this import will become unused and should be removed.

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 2511c9c):

https://flutter-docs-prod--pr13256-fix-copy-no-hidden-wcg56xbe.web.app

[sfshaza2]

LGTM, but I will leave it to you to resolve the bot's complaints.