[TASK] Move LanguageService to EXT:core

The main $GLOBALS['LANG'] class has been moved to the core extension into the "Localization"
namespace, where all other related XLF/XML factory, store and parser classes reside.

This is done in order to streamline the localization of core-relevant files, since this class will
also be used in frontend context.

EXT:lang now contains the backend module, as well as most XLF files.

Resolves: #81196
Releases: master
Change-Id: I0e5d8260f5c5a28254658c68766990b4f4662a2a
Reviewed-on: https://review.typo3.org/52774


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>