LibWeb: Add the search element

[Psychpsyo]

This adds the search element.

[tcl3]

I think I've spotted a couple more places where search elements are mentioned in the spec:

• HTMLParser::is_special_tag() (see: https://html.spec.whatwg.org/multipage/parsing.html#special)
• HTMLElement::default_role() (see: https://www.w3.org/TR/html-aria/#el-search)

If there's a test you could add that exercises the new functionality, that would be great.

[Psychpsyo]

I think I've spotted a couple more places where search elements are mentioned in the spec:

* `HTMLParser::is_special_tag()` (see: https://html.spec.whatwg.org/multipage/parsing.html#special)

* `HTMLElement::default_role()` (see: https://www.w3.org/TR/html-aria/#el-search)

If there's a test you could add that exercises the new functionality, that would be great.

Turns out that we already had the WPT test for this imported and I've just changed the expectations on that one to pass.