[BUGFIX] Ensure copied records keep l10n_state behavior

This change adds a test for localized pages that have
a l10n_source "custom" value (e.g. "pages.author").

When copying the page and its translation,
the l10n_state field is then set to "source",
which is wrong.

copyRecord() sets l10n_source=0, however DataMapItem
expects "null". The patch makes DataMapItem understand
0 as value for l10n_source as well.

Resolves: #88974
Releases: main, 12.4
Change-Id: I326765d92ea52bb49d94bc4965b998b993b5e673
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80518


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: J�rg B�sche <typo3@joergboesche.de>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>