clippy: fix several lint warns (#32126)

As seems #31500 still remain opened here's the next partial fix.

Fixed list: `unused_mut`, `clippy::needless_borrow`,
`clippy::match_ref_pats`, `clippy::borrow_deref_ref`, `clippy::ptr_eq`,
`clippy::unnecessary_cast`, `clippy::derivable_impls`,
`clippy::collapsible_match`, `clippy::extra_unused_lifetimes`,
`clippy::map_clone`, `clippy::manual_filter`.


- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes are part of #31500.
- [x] These changes do not require tests because are only cosmetic.

components/script/dom/customelementregistry.rs

@@ -51,20 +51,15 @@ use crate::script_runtime::JSContext;
 use crate::script_thread::ScriptThread;
 
 /// <https://dom.spec.whatwg.org/#concept-element-custom-element-state>
-#[derive(Clone, Copy, Eq, JSTraceable, MallocSizeOf, PartialEq)]
+#[derive(Clone, Copy, Default, Eq, JSTraceable, MallocSizeOf, PartialEq)]
 pub enum CustomElementState {
     Undefined,
     Failed,
+    #[default]
     Uncustomized,
     Custom,
 }
 
-impl Default for CustomElementState {
-    fn default() -> CustomElementState {
-        CustomElementState::Uncustomized
-    }
-}
-
 /// <https://html.spec.whatwg.org/multipage/#customelementregistry>
 #[dom_struct]
 pub struct CustomElementRegistry {