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>

Cargo.lock

@@ -1172,6 +1172,7 @@ dependencies = [
  "stylo_traits",
  "tracing",
  "webgpu",
+ "webgpu_traits",
  "webrender",
  "webrender_api",
  "webrender_traits",
@@ -6378,6 +6379,7 @@ dependencies = [
  "uuid",
  "webdriver",
  "webgpu",
+ "webgpu_traits",
  "webrender_api",
  "webrender_traits",
  "webxr-api",
@@ -6501,10 +6503,11 @@ dependencies = [
  "stylo_traits",
  "uuid",
  "webdriver",
- "webgpu",
+ "webgpu_traits",
  "webrender_api",
  "webrender_traits",
  "webxr-api",
+ "wgpu-core",
 ]
 
 [[package]]
@@ -8567,6 +8570,7 @@ dependencies = [
  "serde",
  "servo_config",
  "servo_malloc_size_of",
+ "webgpu_traits",
  "webrender",
  "webrender_api",
  "webrender_traits",
@@ -8574,6 +8578,20 @@ dependencies = [
  "wgpu-types",
 ]
 
+[[package]]
+name = "webgpu_traits"
+version = "0.0.1"
+dependencies = [
+ "arrayvec",
+ "base",
+ "ipc-channel",
+ "serde",
+ "servo_malloc_size_of",
+ "webrender_api",
+ "wgpu-core",
+ "wgpu-types",
+]
+
 [[package]]
 name = "webpki-roots"
 version = "0.26.8"