Consider replacing deprecated `clip`

[janbrasna]

Description

The visually-hidden helper includes an outdated syntax of clip: rect() that may need replacing with some other clipping properties or maybe updating the helper to something more current overall.

Steps to reproduce

The next stylelint-config-standard-scss major version won't like it.

😭 /actions/runs/17982808350/job/51153182926 ✂️

Expected result

https://developer.mozilla.org/en-US/docs/Web/CSS/clip

Actual result

protocol/assets/sass/protocol/includes/mixins/_utils.scss

Lines 128 to 133 in 81e6c70

	@mixin visually-hidden {
	border: 0;
	clip: rect(0 0 0 0);
	height: 1px;
	margin: -1px;
	overflow: hidden;

Environment

This might be breaking of sorts, in case a consumer applies the mixin, but then e.g. redefines or undoes the visual hiding in some cases, changing the clip value there — so there might be a migration to the newer mixin content version necessary for them.

• https://github.com/mozilla/bedrock/blob/2025-09-24/media/css/m24/components/footer-refresh.scss#L412
• https://github.com/mozilla/bedrock/blob/2025-09-24/media/css/firefox/whatsnew/whatsnew-142.scss#L1564