Description
When adding or modifying a url in the button block, the user can enter anything, there's no validation or feedback about whether the URL has any errors, or even about whether the URL was successfully added.

There's also no audible feedback for screenreader users.

Tasks:

• Add the same URL validation that's present in the paragraph block's link format to the button block.
• Ensure there's sufficient visual feedback for users about whether the link was successfully added or whether it might contain errors.
• Ensure there's audible feedback for screen reader users (e.g. using the speak functionality).

Additional Details
Discovered in #10128, but is an issue present since the launch of the button block.