Auto merge of #11639 - awestroke:anchor-element-base-url, r=nox

Use base_url instead of url in HTMLAnchorElement::set_url

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`script::dom::HTMLAnchorElement::set_url` now uses `document::base_url` instead of `document::url`, allowing correct parsing of relative urls on about:blank and pages with a `<base href="some_url"/>` set.

spec: https://html.spec.whatwg.org/multipage/infrastructure.html#resolving-urls

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #11628

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- [x] There are tests for these changes: Some expected test failures have been removed.

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