[BUGFIX] Send specific value when unchecking items in TypoScript module

Using `GlobalEventHandler` in combination with checkboxes and unchecking
on item uses and empty string `''` as value for that particular parameter
(e.g. `&setting=`). However, some scenarios in the TYPO3 backend rely on
receiving `&setting=0` instead - e.g. see BackendUtility::getModuleData().

New attribute `data-empty-value` has been introduced to achieve that.

Resolves: #92378
Releases: master, 10.4
Change-Id: Idc372b8c572212fc26cf2bae7fa6e74c2a2a9c59
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65832


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Richard Haeser <richard@richardhaeser.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Richard Haeser <richard@richardhaeser.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>