[css-ui] Remove appearance: slider-vertical carefully

[AutoSponge]

• https://www.w3.org/TR/css-ui-4/#appearance-switching
• Rendering <input type=range> vertically whatwg/html#4177
• see [css-ui] Consider removing slider-horizontal from <compat-auto> #8506

If slider-vertical is removed, as similar values in #8506, please include usage numbers so APA can weigh in. The accessibility concern here is that Chromium generates a UA assigned orientation: vertical (see the accessibility viewer in devtools). The default orientation for a range/slider is horizontal. This is normally the domain of aria-orientation and any current usage of appearance: slider-vertical may be depending on these UA-supplied semantics to convey the orientation.

EDIT: Since the WHATWG conversation was around writing direction, i18n may also want to weigh in.

[zcorpan]

Usage per Chrome's use counter is currently ~0.0045% of page views: https://chromestatus.com/metrics/feature/timeline/popularity/2570

[yisibl]

Chrome will be deprecated here: https://bugs.chromium.org/p/chromium/issues/detail?id=1426629