Bump xmldom and web-ext

Removes [xmldom](https://github.com/xmldom/xmldom). It's no longer used after updating ancestor dependency [web-ext](https://github.com/mozilla/web-ext). These dependencies need to be updated together.


Removes `xmldom`

Updates `web-ext` from 2.9.3 to 7.2.0
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@2.9.3...7.2.0)

---
updated-dependencies:
- dependency-name: xmldom
  dependency-type: indirect
- dependency-name: web-ext
  dependency-type: direct:development
...

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