Fix radio group validity update when removing or selecting an input (#36252)

This PR fixes an issue where radio inputs in the same group failed to
correctly update their `validity.valueMissing` state when:

- A **checked radio button was removed** from the DOM.
- A **different radio button was selected** by user interaction.

This behavior caused mismatches with how browsers like Firefox handle
radio group validation.

---

### Changes in This PR

#### Radio group revalidation on DOM removal
- Updated `unbind_from_tree()` to revalidate other radio buttons in the
same group when a checked input is removed.
- Uses `UnbindContext::parent` as the DOM root to ensure the correct
context is used during traversal.

#### New helper: `find_related_radios()`
- Encapsulates logic for finding other inputs in the same group.
- Used during both removal and attribute changes for consistency.

#### Validation on `checked`/`value` updates
- Introduced `update_related_validity_states()` to revalidate all group
members when a radio's `checked` or `value` is changed.

#### Web Platform Test (WPT) coverage
- Created a new WPT file: `radio-group-valueMissing.html`.
- Tests follow recommended `test()` pattern:
  - **Precondition**: Assert initial `valueMissing`.
  - **Action**: Remove or select a radio.
  - **Postcondition**: Assert expected `valueMissing`.

#### Manifest updated
- The WPT manifest now includes the new test.

---
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- [X] `./mach build -d` does not report any errors
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- [X] These changes fix #36110

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Signed-off-by: Emmanuel Elom <elomemmanuel007@gmail.com>

components/script/dom/activation.rs

@@ -16,12 +16,17 @@ pub(crate) trait Activatable {
     fn is_instance_activatable(&self) -> bool;
 
     // https://dom.spec.whatwg.org/#eventtarget-legacy-pre-activation-behavior
-    fn legacy_pre_activation_behavior(&self) -> Option<InputActivationState> {
+    fn legacy_pre_activation_behavior(&self, _can_gc: CanGc) -> Option<InputActivationState> {
         None
     }
 
     // https://dom.spec.whatwg.org/#eventtarget-legacy-canceled-activation-behavior
-    fn legacy_canceled_activation_behavior(&self, _state_before: Option<InputActivationState>) {}
+    fn legacy_canceled_activation_behavior(
+        &self,
+        _state_before: Option<InputActivationState>,
+        _can_gc: CanGc,
+    ) {
+    }
 
     // https://dom.spec.whatwg.org/#eventtarget-activation-behavior
     // event and target are used only by HTMLAnchorElement, in the case