Draft: Remove jQuery dependency from dom.js

What does this MR do and why?

Removes jQuery calls from dom.js, a helper script that provides a few DOM-related utilities.

jQuery was only used here for getting the outer height of the collapsible_container component (used for the table of contents on small-width devices). It's now a lot easier to get the outer height of elements without jQuery: https://youmightnotneedjquery.com/#outer_height

One step towards closing #1682 (closed) 🚶

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md.
2. Size your window down below the XL breakpoint, where the mobile nav kicks in
3. Verify you can expand and collapse the table of contents component (the list of items under "on this page")

Merge request acceptance checklist

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