No tracing of nop traceable fields (#29926)

* Add `no_trace` option to JSTraceable derive

* NoTrace wrapper

* Port some types to no_trace schematics

* Fixing my unsafe mistakes (not tracing traceables)

* Add docs & safety guards for no_trace

Safety guards (trait shenanigans) guarantees safety usage of `no_trace`

* Port canvas_traits to no_trace

* Port servo_media to no_trace

* Port net_traits to no_trace

* Port style to no_trace

* Port webgpu to no_trace

* Port script_traits to no_trace

* Port canvas_traits, devtools_traits, embedder_traits, profile_traits to no_trace

* unrooted_must_root lint in seperate file

* Add trace_in_no_trace_lint as script_plugin

* Composable types in must_not_have_traceable

* Introduced HashMapTracedValues wrapper

* `HashMap<NoTrace<K>,V>`->`HashMapTracedValues<K,V>`

* Port rest of servo's types to no_trace

* Port html5ever, euclid, mime and http to no_trace

* Port remaining externals to no_trace

* Port webxr and Arc<Mutex<_>>

* Fix spelling in notrace doc

components/script/dom/canvasgradient.rs

@@ -22,13 +22,14 @@ use dom_struct::dom_struct;
 pub struct CanvasGradient {
     reflector_: Reflector,
     style: CanvasGradientStyle,
+    #[no_trace]
     stops: DomRefCell<Vec<CanvasGradientStop>>,
 }
 
 #[derive(Clone, JSTraceable, MallocSizeOf)]
 pub enum CanvasGradientStyle {
-    Linear(LinearGradientStyle),
-    Radial(RadialGradientStyle),
+    Linear(#[no_trace] LinearGradientStyle),
+    Radial(#[no_trace] RadialGradientStyle),
 }
 
 impl CanvasGradient {