Major pain point is that I had to write the bitfield stuff manually, but that
should be resolved soon again.
Now we generate proper layout for _every_ struct, including field offsets \o/.
Add Element.style support for stylo
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This is the Servo side change of [bug 1294299](https://bugzilla.mozilla.org/show_bug.cgi?id=1294299) which has been reviewed by @heycam, @emilio, and @SimonSapin.
This should not be merged until the Gecko side change gets merged into mozilla-central.
r? @heycam
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