style: Use cbindgen to back CSS transforms.

This avoids the expensive conversion, and cleans up a bunch.

Further cleanup is possible, just not done yet to avoid growing the patch even
more.

Differential Revision: https://phabricator.services.mozilla.com/D30748

components/style/values/computed/angle.rs

@@ -26,6 +26,7 @@ use style_traits::{CssWriter, ToCss};
     ToAnimatedZero,
     ToResolvedValue,
 )]
+#[repr(C)]
 pub struct Angle(CSSFloat);
 
 impl ToCss for Angle {