[BUGFIX] Show hidden subgroups of fe_group

When editing a fe_group show its subgroups even if those are set to
hidden in order to avoid losing the subgroup relation on saving the
fe_group.

Resolves: #87649
Releases: master, 9.5
Change-Id: Ic39f32b47327202a848827bd9d6b4935c35edcdd
Reviewed-on: https://review.typo3.org/59640


Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Tested-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>