feat(ui5-checkbox): enable font-size based scaling for standalone checkboxes

[NakataCode]

Implement font-size based scaling for standalone CheckBox components, allowing developers to easily resize checkboxes by setting CSS font-size and removing the padding by setting it to 0.

🎯 Changes

• CheckBox now scales proportionally based on font-size value
• All visual elements scale uniformly (box, checkmark, focus outline)
• Padding can be controlled independently for spacing adjustments
• Maintains perfect proportions across all sizes

Usage Example

<ui5-checkbox style="font-size: 32px; padding: 0;"></ui5-checkbox>

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-13021--ui5-webcomponents-preview.netlify.app

[dobrinyonkov]

Looks, good so far. Let's also add a sample in the dev samples here https://pr-13021--ui5-webcomponents-preview.netlify.app/packages/main/test/pages/CheckBox.html

and perhaps a test to test font-size on the host actually increases the .ui5-checkbox-inner.offsetWidth/Height and related elements - icon, tri-state box, ect.