style: Update cbindgen.

This cleans up the pattern of "Use a private dtor so that the helper functions
do the right thing" by enabling it everywhere using:

  https://github.com/eqrion/cbindgen/pull/377

It also caught some uninitialized value issues.

I think they're mostly harmless since we zero-initialize our structs:

https://searchfox.org/mozilla-central/rev/325c1a707819602feff736f129cb36055ba6d94f/servo/components/style/properties/gecko.mako.rs#632

And since we override the clip rect, which is the other bit of code that was
failing to build with this change.

Differential Revision: https://phabricator.services.mozilla.com/D43491

components/style/values/specified/text.rs

@@ -132,7 +132,6 @@ impl ToComputedValue for LineHeight {
 }
 
 /// A generic value for the `text-overflow` property.
-/// cbindgen:derive-tagged-enum-copy-constructor=true
 #[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
 #[repr(C, u8)]
 pub enum TextOverflowSide {