Migrate to parse5/tools

[43081j]

This removes the dom5 copy we've been keeping around in modernweb, and instead uses the parse5/tools package (from parse5 org itself).

TODO: parse5/tools is an esm-only package, so this build fails right now as the mw packages all seem to target cjs. we may need to change everything to publishing esm before this can land... 😞 thoughts @Westbrook ?

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[Westbrook]

I’m all for moving to 100% esm, but I’m not envious of anyone willing to take on that work.