[!!!][TASK] Make language module part of install extension

The language module changes configuration files and basic
instance system files and thus belongs to the install extension.

The patch moves the "Admin Tools" -> "Language" module to
"Maintenance" -> "Manage language packs" and comes with a
series of advantages:
* UX improvements and better overview
* Overall language pack update progress is much quicker
* Just a fraction of code needed
* No dependency to extension manager anymore
* Documentation extension has no hidden dependency to lang anymore

Change-Id: Ibcb9659dfacb5fda7c00ab2f39160f095e0cd154
Resolves: #84131
Releases: master
Reviewed-on: https://review.typo3.org/55998


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Tobi Kretschmann <tobi@tobishome.de>
Tested-by: Tobi Kretschmann <tobi@tobishome.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>