Add shadowrootclonable attribute

[pepelsbey]

Summary

Adds

• shadowrootclonable attribute
• shadowRootClonable IDL attribute

for template element.

Test results and supporting details

Currently supported only in Chrome Canary, expected to ship in Chrome 124.

Quick test

<p>outer</p>
<div>
    <template shadowrootmode="open" shadowrootclonable>
        <p>inner</p>
    </template>
</div>
<script>
    const div = document.querySelector('div');
    const clone = div.cloneNode();
    document.body.appendChild(clone);
</script>

See Chrome Status

[Elchi3]

Confirmed with https://mdn-bcd-collector.gooborg.com/tests/api/HTMLTemplateElement/shadowRootClonable in Chrome 124 beta, so we might as well put 124 here.

[Elchi3]

Thanks! 👍