[TASK] Extend Regular DataHandler functional tests

* add third tt_content element with localization in live context
* populate changes to all scenarios in live and workspace context

Releases: 6.2, 6.3
Resolves: #59881
Change-Id: I644e264048a5c33c0a613d5f8440975cabd40721
[BUGFIX] Failing cascaded delete action of localized elements

Having a record in live workspace with an accordant localization
leads to the fact that actions to the default language also have
an impact to all localizations.

In a workspace, first deleting the localization, then deleting
the record of the default language, ends up in actually having
reverted the previous deletion of the localization.

The solution is to check for delete placeholders in
DataHandler::deleteL10nOverlayRecords().

Resolves: #59113
Releases: 6.2, 6.3
Change-Id: I888c83a58d591f57bc2ea75a49fa603a56a7f722