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/script/dom/window.rs

@@ -21,7 +21,10 @@ use base64::Engine;
 #[cfg(feature = "bluetooth")]
 use bluetooth_traits::BluetoothRequest;
 use canvas_traits::webgl::WebGLChan;
-use constellation_traits::{ScrollState, WindowSizeType};
+use constellation_traits::{
+    DocumentState, LoadData, LoadOrigin, NavigationHistoryBehavior, ScriptToConstellationChan,
+    ScriptToConstellationMessage, ScrollState, StructuredSerializedData, WindowSizeType,
+};
 use crossbeam_channel::{Sender, unbounded};
 use cssparser::{Parser, ParserInput, SourceLocation};
 use devtools_traits::{ScriptToDevtoolsControlMsg, TimelineMarker, TimelineMarkerType};
@@ -62,10 +65,7 @@ use script_layout_interface::{
     FragmentType, Layout, PendingImageState, QueryMsg, Reflow, ReflowGoal, ReflowRequest,
     TrustedNodeAddress, combine_id_with_fragment_type,
 };
-use script_traits::{
-    DocumentState, LoadData, LoadOrigin, NavigationHistoryBehavior, ScriptThreadMessage,
-    ScriptToConstellationChan, ScriptToConstellationMessage, StructuredSerializedData,
-};
+use script_traits::ScriptThreadMessage;
 use selectors::attr::CaseSensitivity;
 use servo_arc::Arc as ServoArc;
 use servo_config::{opts, pref};