Description

This seems to be an issue in both the front-end and editor. When using a screen reader, the button isn't properly announced when focused.

Step-by-step reproduction instructions

1. Add a search block
2. Use the icon button option form the toolbar
3. Using a screenreader, focus the button

Expected: The button is announced with default text as the aria label, like 'Submit search'
Actual: It doesn't get announced properly

Environment info

• Mac OS / Safari / Voiceover
• Latest Gutenberg trunk

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes