[TASK] Cleanup various LanguageService-related code

Over the past few commits, a lot of changes
happened with LanguageService-related code, mainly
to streamline the initialization and creation
of LanguageService code.

For this reason, various parts have now been sorted
out:
* Proper injection of Locales class
* Consistent usage of LanguageService->init()
* Avoid additional pageRendererSetupTrait call in LoginController
* Avoid using LanguageService->init() if Factory is used
* Leftover "ISOcode" value is removed

Resolves: #99693
Releases: main
Change-Id: Ib4bbc5b38505d712c86eb7e6a3c8455ba49225de
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77557


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Susanne Moog <look@susi.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Benni Mack <benni@typo3.org>