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/properties/longhands/box.mako.rs

@@ -352,7 +352,6 @@ ${helpers.predefined_type(
     "generics::transform::Transform::none()",
     extra_prefixes=transform_extra_prefixes,
     animation_value_type="ComputedValue",
-    gecko_ffi_name="mSpecifiedTransform",
     flags="CREATES_STACKING_CONTEXT FIXPOS_CB \
            GETCS_NEEDS_LAYOUT_FLUSH CAN_ANIMATE_ON_COMPOSITOR",
     spec="https://drafts.csswg.org/css-transforms/#propdef-transform",

components/style/properties/longhands/ui.mako.rs

@@ -81,7 +81,6 @@ ${helpers.predefined_type(
     "Transform",
     "generics::transform::Transform::none()",
     products="gecko",
-    gecko_ffi_name="mSpecifiedWindowTransform",
     flags="GETCS_NEEDS_LAYOUT_FLUSH",
     animation_value_type="ComputedValue",
     spec="None (Nonstandard internal property)",