[TASK] Add visually hidden label to the search buttons

To trigger a search, usually an icon-only button is placed next to the
search input field. To improve the accessibility of these icon-only
buttons, a visually hidden label is added.

Resolves: #102410
Releases: main, 12.4
Change-Id: Ifd7faee3d4c727dd2e86ad7304e19f970b61699e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83835


Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Willi Wehmeier <wwwehmeier@gmail.com>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>