feat(radio): add shadow part for label (#28607)

Issue number: Part of #28300 

---------

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
Developers are unable to adjust margin, width, etc. of the radio label

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- Radio label has a shadow part.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->
As part of this work, I investigated moving `pointer-events: none` up
the DOM tree so developers wouldn't be able to override it with the
shadow part. In my testing, I was unable to see any difference in
behavior with vs without `pointer-events: none`. Therefore, I removed it
entirely.

core/src/components/radio/radio.scss

@@ -109,13 +109,6 @@ input {
 // ----------------------------------------------------------------
 
 .label-text-wrapper {
-  /**
-   * This ensures that double tapping this text
-   * clicks the <label> and focuses the radio
-   * when a screen reader is enabled.
-   */
-  pointer-events: none;
-
   text-overflow: ellipsis;
 
   white-space: nowrap;

core/src/components/radio/radio.tsx

@@ -15,6 +15,7 @@ import type { Color, StyleEventDetail } from '../../interface';
  * @slot - The label text to associate with the radio. Use the "labelPlacement" property to control where the label is placed relative to the radio.
  *
  * @part container - The container for the radio mark.
+ * @part label - The label text describing the radio.
  * @part mark - The checkmark or dot used to indicate the checked state.
  */
 @Component({
@@ -297,6 +298,7 @@ export class Radio implements ComponentInterface {
               'label-text-wrapper': true,
               'label-text-wrapper-hidden': !hasLabel,
             }}
+            part="label"
           >
             <slot></slot>
           </div>

core/src/components/radio/test/radio.spec.ts

@@ -31,6 +31,23 @@ describe('ion-radio', () => {
 
     expect(radio.classList.contains('radio-checked')).toBe(true);
   });
+
+  it('should render the radio with shadow parts', async () => {
+    const page = await newSpecPage({
+      components: [Radio, RadioGroup],
+      html: `
+        <ion-radio-group>
+          <ion-radio value="value"></ion-radio>
+        </ion-radio-group>
+      `,
+    });
+
+    const radio = page.body.querySelector('ion-radio')!;
+
+    expect(radio).toHaveShadowPart('container');
+    expect(radio).toHaveShadowPart('label');
+    expect(radio).toHaveShadowPart('mark');
+  });
 });
 
 describe('ion-radio: disabled', () => {