fix(overlays): focus management with checkbox/radio (#30026)

Issue number: resolves internal

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## What is the current behavior?
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Using `Tab` or `Shift + Tab` to focus through elements in a modal won't
behave as expected when using `ion-checkbox` or `ion-radio` within an
`ion-item`. Previously, the behavior would result in the last item in a
list getting focus styling, but `document.activeElement` would still be
the first actionable item in the overlay

## What is the new behavior?
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this PR. -->

For checkboxes, the `ion-checkbox` element itself will be focused rather
than the encapsulating `ion-item`

For radios, the `ion-radio-group` will be used to focus the appropriate
element. This will be the first `ion-radio` if there is no "checked"
item, or the "checked" item if one exists.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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