script: Expose node helpers as NodeTraits and give more descriptive names (#34832)

This puts a few commonly used `Node` helpers into a trait (`NodeTraits`)
and gives them more descriptive names and documentation. The renames:

- `document_from_node` -> `NodeTraits::owner_document`
- `window_from_node` -> `NodeTraits::owner_window`
- `stylesheets_owner_from_node<T:` -> `NodeTraits::stylesheet_list_owner`
- `containing_shadow_root` -> `NodeTraits::containing_shadow_root`

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

components/script/layout_image.rs

@@ -21,7 +21,7 @@ use crate::dom::bindings::reflector::DomObject;
 use crate::dom::bindings::root::DomRoot;
 use crate::dom::document::Document;
 use crate::dom::globalscope::GlobalScope;
-use crate::dom::node::{document_from_node, Node};
+use crate::dom::node::{Node, NodeTraits};
 use crate::dom::performanceresourcetiming::InitiatorType;
 use crate::network_listener::{self, PreInvoke, ResourceTimingListener};
 use crate::script_runtime::CanGc;
@@ -97,7 +97,7 @@ pub fn fetch_image_for_layout(
     id: PendingImageId,
     cache: Arc<dyn ImageCache>,
 ) {
-    let document = document_from_node(node);
+    let document = node.owner_document();
     let context = LayoutImageContext {
         id,
         cache,