feat(checkbox): add required prop (#30157)

Issue number: resolves internal

---------

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## What is the current behavior?
- Currently, the screen reader do not announce the component as required
when `required={true}`.

## What is the new behavior?
- Added a new `required` prop to be used for accessibility purposes that
adds the `required` attribute to checkbox's inner native input.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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

@@ -54,3 +54,33 @@ describe('ion-checkbox: indeterminate', () => {
     expect(checkbox.getAttribute('aria-checked')).toBe('mixed');
   });
 });
+
+describe('ion-checkbox: required', () => {
+  it('should have a required attribute in inner input when true', async () => {
+    const page = await newSpecPage({
+      components: [Checkbox],
+      html: `
+        <ion-checkbox required="true">Checkbox</ion-checkbox>
+      `,
+    });
+
+    const checkbox = page.body.querySelector('ion-checkbox')!;
+    const nativeInput = checkbox.shadowRoot?.querySelector('input[type=checkbox]')!;
+
+    expect(nativeInput.hasAttribute('required')).toBeTruthy();
+  });
+
+  it('should not have a required attribute in inner input when false', async () => {
+    const page = await newSpecPage({
+      components: [Checkbox],
+      html: `
+        <ion-checkbox required="false">Checkbox</ion-checkbox>
+      `,
+    });
+
+    const checkbox = page.body.querySelector('ion-checkbox')!;
+    const nativeInput = checkbox.shadowRoot?.querySelector('input[type=checkbox]')!;
+
+    expect(nativeInput.hasAttribute('required')).toBeFalsy();
+  });
+});