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/messaging.rs

@@ -11,6 +11,7 @@ use std::result::Result;
 use base::id::PipelineId;
 #[cfg(feature = "bluetooth")]
 use bluetooth_traits::BluetoothRequest;
+use constellation_traits::ScriptToConstellationMessage;
 use crossbeam_channel::{Receiver, SendError, Sender, select};
 use devtools_traits::{DevtoolScriptControlMsg, ScriptToDevtoolsControlMsg};
 use ipc_channel::ipc::IpcSender;
@@ -18,7 +19,7 @@ use net_traits::FetchResponseMsg;
 use net_traits::image_cache::PendingImageResponse;
 use profile_traits::mem::{self as profile_mem, OpaqueSender, ReportsChan};
 use profile_traits::time::{self as profile_time};
-use script_traits::{Painter, ScriptThreadMessage, ScriptToConstellationMessage};
+use script_traits::{Painter, ScriptThreadMessage};
 use stylo_atoms::Atom;
 use timers::TimerScheduler;
 #[cfg(feature = "webgpu")]