The alias is left there temporarilly and will be removed completely in a later commit where
also components/style/gecko/generated/structs_{debug|release}.rs are re-generated (they still
use the old alias).
We parse when assigning using the namespaces of the stylesheet. It isn't
clear if the spec says to do that (Firefox doesn't support the setter at
all, Chrome does, Safari doesn't); the spec issue is here:
https://github.com/w3c/csswg-drafts/issues/1511
Also fix ToCss implementation of AttrSelectorOperator to not pad with
spaces, to conform with CSSOM. This means we have to update some unit
tests that expect operators with spaces around them in attribute
selectors to roundtrip.
See the "attribute selector" section of "Serializing Selectors" here:
https://drafts.csswg.org/cssom/#serializing-selectors
CSSStyleRule.selectorText is specified here:
https://drafts.csswg.org/cssom/#dom-cssstylerule-selectortext
