misc: include SVG elements by default in typed querySelector

[brendankenny]

fixes #12011

To recap: we need gatherers to deal with svg elements where they overlap in tag names with HTML elements (at least <a>, <script>, <style>, and <title>) since real pages contain those elements and those svg elements have different attributes and behavior than their HTML counterparts (causing bugs like #6481). This PR makes querySelector include those svg elements by default instead of only including them if no matching HTML element was found.

So now document.querySelector('a') returns a value of type HTMLAnchorElement | SVGAElement instead of just HTMLAnchorElement, and the subsequent code has to identify which of the two it's dealing with before proceeding.

However, we also use querySelector a lot in the report (usually via dom.find()), and it's annoying to have to do that extra work when we were also the ones that just wrote the template being queried and it only includes an HTMLAnchorElement. This PR maintains the current behavior of dom.find() to make report authoring easier.

This wasn't quite the idea laid out in #12011 (comment) ("make dom.find() only return HTMLElements (the same way it already filters out null)") because it turns out we already query into svg at least twice in the report (for chevrons and clipping the full-page screenshot), there may be more (e.g. queries without a tag name in them), and there's no strong reason for us to prevent doing any svg querying in the future.

As a result, for dom.find() this PR maintains the old behavior of pretending there's no such thing as an SVGStyleElement (only in the world of the report), assuming that there's no reason we'd ever want an SVGStyleElement in there (you can just style svg from html-level css). If that ever changes, we can always make dom.find() stricter.

[brendankenny]

R: @connorjclark because I'm pretty sure he's the only other person who cares about this :)

[brendankenny]

I'd love to not cast here, but the types aren't quite compatible, testing is totally broken if you try to filter out SVG elements at runtime (jsdom/jsdom#2734), and if you try to do naive filtering of the type, tsc will give you things like HTMLElementTagNameMap[keyof HTMLElementTagNameMap] & HTMLAnchorElement, which, when parameterized, gives you leftovers like SVGAElement & HTMLAnchorElement, which is not the empty set of properties so isn't eliminating anything from the union of types :)

[brendankenny]

typed-query-selector returns unknown from ParseSelectorToTagNames for both situations it can't handle and known error states (like document.querySelector('')). As a result, with Element here it'll still give that type for those bad queries instead of never, but it has to be included for queries like '[alt], [aria-label]' (from page-functions) which need the Element fall back.

Not much to do to get around this except write our own version, but no worse than the current state of things or the default typescript querySelector types :)