Include ServoBindingList.h for binding generating
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See [bug 1296594](https://bugzilla.mozilla.org/show_bug.cgi?id=1296594)
r? @bholley
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- [ ] These changes fix #__ (github issue number if applicable).
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- [ ] There are tests for these changes OR
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This is bug 1296594 on Gecko side.
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This configures the regeneration of atoms as part of the normal generation of
bindings, so it stops being a whole different process.
This also adds a generated file to components/style/generated with a convenience
macro invocation for pseudo-elements, which comes handy in order to avoid
duplication.
