webgpu: Add a webgpu_traits crate (#36320)

This breaks the `script_traits` dependency  on `webgpu`. In general, the
`traits` crates shouldn't depend on Servo non-`traits` crates. This is
necessary to move "script to constellation" messages to the
`constellation_traits` crate, making it the entire API for talking to
the
constellation. This will break a circular dependency when that happens.

Testing: Successfully building is enough of a test for this one as
it is mainly moving types around.

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

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

components/shared/webgpu/messages/to_script.rs

@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! IPC messages that are sent to the ScriptThread.
+
+use base::id::PipelineId;
+use serde::{Deserialize, Serialize};
+use wgpu_core::id::{
+    AdapterId, BindGroupId, BindGroupLayoutId, BufferId, CommandBufferId, ComputePassEncoderId,
+    ComputePipelineId, DeviceId, PipelineLayoutId, QuerySetId, RenderBundleId, RenderPassEncoderId,
+    RenderPipelineId, SamplerId, ShaderModuleId, StagingBufferId, SurfaceId, TextureId,
+    TextureViewId,
+};
+
+use crate::{DeviceLostReason, Error, WebGPUDevice};
+
+#[derive(Clone, Debug, Deserialize, Serialize)]
+pub enum WebGPUMsg {
+    FreeAdapter(AdapterId),
+    FreeDevice {
+        device_id: DeviceId,
+        pipeline_id: PipelineId,
+    },
+    FreeBuffer(BufferId),
+    FreePipelineLayout(PipelineLayoutId),
+    FreeComputePipeline(ComputePipelineId),
+    FreeRenderPipeline(RenderPipelineId),
+    FreeBindGroup(BindGroupId),
+    FreeBindGroupLayout(BindGroupLayoutId),
+    FreeCommandBuffer(CommandBufferId),
+    FreeTexture(TextureId),
+    FreeTextureView(TextureViewId),
+    FreeSampler(SamplerId),
+    FreeSurface(SurfaceId),
+    FreeShaderModule(ShaderModuleId),
+    FreeRenderBundle(RenderBundleId),
+    FreeStagingBuffer(StagingBufferId),
+    FreeQuerySet(QuerySetId),
+    FreeComputePass(ComputePassEncoderId),
+    FreeRenderPass(RenderPassEncoderId),
+    UncapturedError {
+        device: WebGPUDevice,
+        pipeline_id: PipelineId,
+        error: Error,
+    },
+    DeviceLost {
+        device: WebGPUDevice,
+        pipeline_id: PipelineId,
+        reason: DeviceLostReason,
+        msg: String,
+    },
+    Exit,
+}