feat(ui5-link): add default text slot

[hinzzx]

The problem was that the ui5-link component was missing a @slot decorator for its default text slot.

Without this decorator:

• The component didnt invalidate when slot content changed
• The effectiveTabIndex getter (which checks this.textContent?.length) wasn't re-evaluated after text was added
• The initial tabindex of -1 (set during first render when there was no text) remained unchanged

So we add the @slot decorator to the default text slot, following the same pattern used in theui5-button component:

This ensures that:

• When text content is added, removed, or changed in the slot, the component is invalidated
• The component re-renders and recalculates effectiveTabIndex
• The tabindex attribute in the shadow DOM is updated correctly

Before

After

Fixes: #5843

[ui5-webcomponents-bot]

🧹 Preview deployment cleaned up: https://pr-12781--ui5-webcomponents.netlify.app

[ui5-webcomponents-bot]

🎉 This PR is included in version v2.18.0-rc.0 🎉

The release is available on v2.18.0-rc.0

Your semantic-release bot 📦🚀

[ui5-webcomponents-bot]

🎉 This PR is included in version v2.18.0 🎉

The release is available on v2.18.0

Your semantic-release bot 📦🚀