Add lots of derived Debug impls
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Add a bunch of derived `Debug` impls. After this, pretty much anything that implements `Deserializable` also implements `Debug`. The exception is `webrender_api::RenderApiSender`, which would need a webrender PR.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because it's just debugging
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This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/22028)
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a59a80b301
