Auto merge of #13108 - emilio:stupidest-opt-ever, r=bholley

style: Don't loop over all the set of dependencies always.

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Instead, divide which kind of dependencies could match a mutation. This cuts down incremental restyle time in BrowserHTML quite a bit.

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The dependency count is not at all minor, and this way we avoid looping
through all of them in the common cases, mainly either changing state, or
attributes.

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