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/compositing/compositor.rs

@@ -20,14 +20,13 @@ use compositing_traits::{
     CompositionPipeline, CompositorMsg, CompositorReceiver, SendableFrameTree,
 };
 use constellation_traits::{
-    AnimationTickType, CompositorHitTestResult, EmbedderToConstellationMessage, PaintMetricEvent,
-    UntrustedNodeAddress, WindowSizeType,
+    AnimationTickType, EmbedderToConstellationMessage, PaintMetricEvent, WindowSizeType,
 };
 use crossbeam_channel::Sender;
 use dpi::PhysicalSize;
 use embedder_traits::{
-    Cursor, InputEvent, MouseButtonEvent, MouseMoveEvent, ScreenGeometry, ShutdownState,
-    TouchEventType, ViewportDetails,
+    AnimationState, CompositorHitTestResult, Cursor, InputEvent, MouseButtonEvent, MouseMoveEvent,
+    ScreenGeometry, ShutdownState, TouchEventType, UntrustedNodeAddress, ViewportDetails,
 };
 use euclid::{Box2D, Point2D, Rect, Scale, Size2D, Transform3D};
 use fnv::FnvHashMap;
@@ -37,7 +36,6 @@ use log::{debug, info, trace, warn};
 use pixels::{CorsStatus, Image, ImageFrame, PixelFormat};
 use profile_traits::time::{self as profile_time, ProfilerCategory};
 use profile_traits::time_profile;
-use script_traits::AnimationState;
 use servo_config::opts;
 use servo_geometry::DeviceIndependentPixel;
 use style_traits::{CSSPixel, PinchZoomFactor};