Auto merge of #14922 - heycam:pseudo-inherit, r=emilio

Don't inherit all properties for eagerly computed pseudos if there are no matching rules.

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When we resolve style for an eagerly computed pseudo-element, such as an anonymous box, if there are no matching rules we currently just clone the parent's style.  We should only do that if `inherit_all` is true, otherwise we should inherit only the inherited properties from the parent.

I was going to use `.unwrap_or_default()` on the result of looking up `precomputed_pseudo_element_decls`, but that didn't seem to work since that map lookup returns a reference and not a `Vec` itself.

r? @emilio

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- [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1329121

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