Confirmdialog: add custom button text

[chad1008]

Description

Follow up to #37602 (comment), this PR adds the ability to set custom label text for the confirm and cancel buttons in the experimental ConfirmDialog component.

cc @fullofcaffeine @ciampo

Testing Instructions

• Launch Storybook locally
• locate the ConfirmDialog component and select the new 'With Custom Button Labels" Story
• manipulate the new "cancel button" and "confirm button" knobs to test different text strings
• make sure all components tests pass, as this PR also adds a new test to confirm the specified button text is being rendered

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.

[mirka]

Nice enhancement! If you could update the component readme and add a changelog entry that would be great.

Comments are mostly code health stuff — I thought you'd might want some context around the general components work that's going on, given your interest in the squad 🙌

[chad1008]

Component readme and changelog updated (7c46610) ✅

[mirka]

Looks like we're in good shape!