fix(ui5-user-settings-dialog): announce search results to screen readers

[SvilenDarvenyashki]

• Added an ARIA live-region announcement (InvisibleMessage, Polite mode) that fires whenever the search value changes.
• The announcement reflects the number of matching items:
  • 0 results → "No search results"
  • 1 result → "1 result available"
  • more than 1 → "{count} results are available"
• Added the corresponding i18n message keys to the message bundle.
• Added Cypress tests covering the no-result, single-result, and multiple-result announcements.
• Added Cypress tests covering the no-result, single-result, and multiple-result
  announcements.

[sap-ui5-webcomponents-release]

🚀 Deployed on https://pr-13946--ui5-webcomponents-preview.netlify.app