[BUGFIX] Allow keyboard usage of file upload dropzone

The dropzone for file uploads now uses two <button> tags
instead of <div> tags. One for the dropzone itself and
the other one for the close button.

The dropzone button now has got an `aria-labelledby`
attribute pointing to the dropzone title. The close
button got an `aria-label` attribute. Both to support
screen readers.

Resolves: #92680
Releases: master, 10.4
Change-Id: I32ce15dfc8c36c6fbfd17ef993ceacb8e5aaf3e0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66270


Tested-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Haupt <mail@danielhaupt.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>
Reviewed-by: Daniel Haupt <mail@danielhaupt.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>