Move ScriptToConstellationMsg to constellation_traits (#36364)

This is the last big change necessary to create the
`constellation_traits` crate. This moves the data structure for messages
that originate from the `ScriptThread` and are sent to the
`Contellation` to `constellation_traits`, effectively splitting
`script_traits` in half. Before, `script_traits` was responsible for
exposing the API of both the `ScriptThread` and the `Constellation` to
the rest of Servo.

- Data structures that are used by `ScriptToConstellationMsg` are moved
  to `constellation_traits`. The dependency graph looks a bit like this:
  `script_layout_interface` depends on `script_traits` depends on
  `constellation_traits` depends on `embedder_traits`.
- Data structures that are used in the embedding layer
  (`UntrustedNodeAddress`, `CompositorHitTestResult`, `TouchEventResult`
  and `AnimationState`) are moved to embedder_traits, to avoid a
  dependency cycle between `webrender_traits` and
  `constellation_traits`.
- Types dealing with MessagePorts and serialization are moved to
  `constellation_traits::message_port`.

Testing: This is covered by existing tests as it just moves types
around.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/shared/script_layout/lib.rs

@@ -18,8 +18,8 @@ use app_units::Au;
 use atomic_refcell::AtomicRefCell;
 use base::Epoch;
 use base::id::{BrowsingContextId, PipelineId, WebViewId};
-use constellation_traits::{ScrollState, UntrustedNodeAddress};
-use embedder_traits::ViewportDetails;
+use constellation_traits::{LoadData, ScrollState};
+use embedder_traits::{UntrustedNodeAddress, ViewportDetails};
 use euclid::default::{Point2D, Rect};
 use fnv::FnvHashMap;
 use fonts::{FontContext, SystemFontServiceProxy};
@@ -31,7 +31,7 @@ use net_traits::image_cache::{ImageCache, PendingImageId};
 use pixels::Image;
 use profile_traits::mem::Report;
 use profile_traits::time;
-use script_traits::{InitialScriptState, LoadData, Painter, ScriptThreadMessage};
+use script_traits::{InitialScriptState, Painter, ScriptThreadMessage};
 use serde::{Deserialize, Serialize};
 use servo_arc::Arc as ServoArc;
 use servo_url::{ImmutableOrigin, ServoUrl};