Add support for prefers-contrast CSS config (for isDisabled contrast adjustments)

[patcon]

First off, regardless of whether there's time to engage with this, I wanted to say that I really appreciate your prioritization of accessibility :) I work in the Government of Canada, and am glad to work on a team where it's likely I'll be able to work on some of this upstream stuff! https://react-select.com/advanced#accessibility

Right now, isDisabled on Select component means the current value is very low contrast. This can make it hard to see what the current selection is, even if it can't be changed.

This is a-ok at the moment according to WCAG 2.1 accessibility guidelines, but likely to be adjusted later[1]. We could get ahead of this by allowing small changes in styling based the prefers-contrast CSS media feature that users set in the browser.

The prefers-contrast CSS media feature is used to detect whether the user has requested the web content to be presented with a lower or higher contrast.

-- MDN Docs: prefers-contrast https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-contrast

Open Questions

1. Is this a feature request or a bug for issues? (I know some teams consider accessibility related stuff "bugs", but this is on the line regardless.
2. I recognize that there's already a very powerful and well-considered theming system in react-select, but could CSS media features like this work right now? If not, would it be simple or hard to add it? Would there be openness to accepting a more concrete proposal?
3. More generally, does this sort use of CSS media features (prefers-constrast, prefers-reduced-motion, etc) feel like it would belong upstream within the library?

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[1] The decision to exempt inactive controls from the contrast requirements was based on a number of considerations. Although it would be benefitial to some people to discern inactive controls, a one-size-fits-all solution has been very difficult to establish. A method of varying the presentation of disabled controls, such as adding an icon for disabled controls, based on user preferences is anticipated as an advancement in the future.

-- WCAG 2.1: Inactive User Interface Components
https://www.w3.org/WAI/WCAG21/Understanding/non-text-contrast.html#:~:text=The%20decision%20to,in%20the%20future.

WCAG 3.0: https://www.w3.org/TR/wcag-3.0/ (not seeing any equivalent mention of "inactive" or "non-text contrast", though still early in the expansion of that doc and associated resources)