style: Use serde to serialize LengthPercentage and StyleRayFunction.

We need to pass these two types into the compositor, so we need a better
way to serialize these rust types. We use serde and bincode to
serialize/deserialize them, and use ByteBuf to pass the &[u8] data
through IPC. We define StyleVecU8 for FFI usage only.

Differential Revision: https://phabricator.services.mozilla.com/D50688

components/style_traits/values.rs

@@ -507,7 +507,9 @@ pub mod specified {
 
     /// Whether to allow negative lengths or not.
     #[repr(u8)]
-    #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, PartialOrd, ToShmem)]
+    #[derive(
+        Clone, Copy, Debug, Deserialize, Eq, MallocSizeOf, PartialEq, PartialOrd, Serialize, ToShmem,
+    )]
     pub enum AllowedNumericType {
         /// Allow all kind of numeric values.
         All,