Implement document load cancellation
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Implement update source set & select image source
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Allow supported window attributes to be replacable.
As seen in https://github.com/servo/servo/pull/21045 some Window attributes don't support JavaScript from being able to shadow and replace their values.
This PR adds all other attributes I could find that are supported by servo to be replaceable.
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textarea minLength/maxLength
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textarea minLength/maxLength
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Let the popstate and hashchange events not bubble
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fix#21063
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Implement window.length DOM attribute.
Implements the `window.length` DOM attribute for enumerating frames on the document.
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Allow window.parent attribute to be replaceable by JavaScript.
Permit JS to override the window.parent attribute.
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