[TASK] Use shorthand syntax for global variable $LANG consistently

TYPO3 uses $GLOBALS['LANG'] directly in some places, but since
TYPO3 v7, new code started to use a short hand protected method
"getLanguageService" in order to get IDE code completion and better
analysis of code.

This patch replaces all left-over places of $GLOBALS['LANG']
and encapsulates this into a short-hand method to streamline
TYPO3 Core's code base.

Resolves: #87571
Releases: master
Change-Id: Ie15e320713fe65d40552a19e0a517d5739abbb41
Reviewed-on: https://review.typo3.org/59578


Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>