[BUGFIX] Sort and limit available locales in SiteLanguage selection

When showing the available locales in the SiteLanguage
configuration, the selection is now sorted and also filtered,
by only showing "de_DE" and skipping locales with modifiers,
such as "de_DE.UTF-8" or "de_DE.ISO8859-1" in order to make
life easier for integrators.

Resolves: #99923
Related: #93651
Releases: main, 11.5
Change-Id: I03b38bb19207615e82a7f7917037aad0ac26b997
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77756


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>