next: Refactor is-mobile hook to use new MediaQuery class

[Wombosvideo]

Prerequisites

• This feature already exists in shadcn/ui - if not, it won't be considered here so don't continue with your issue.

Describe the feature

Hey, since the Svelte team added the MediaQuery class, the IsMobile hook is now somewhat redundant.

To keep compatibility with all dependent components, I suggest extending the MediaQuery class:

import { MediaQuery } from "svelte/reactivity";

const MOBILE_BREAKPOINT = 768;

export class IsMobile extends MediaQuery {
	constructor() {
		super(`(max-width: ${MOBILE_BREAKPOINT - 1}px)`);
	}
}

Notice that this might be a breaking change for users refusing to update their dependencies.

But since next is still next and not main, this change is acceptable in my opinion.