This bundles ally.js into Next.js itself to upgrade a dependency they have pinned.

I tried every other major focus trap solution, even those used by some modal libraries, and they all failed.

`ally.js` is the only library that can do it correctly, so we're going to stick with it.

I also removed the `maintain/disabled` as we have a backdrop that would effectively result in the same. This reduces CPU strain.

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Fixes #19893
Fixes #14369
Closes #14372