[TASK] Switch Locales to regular singleton instance

Locales resolves the user-defined TYPO3-languages and
its dependencies via TYPO3_CONF_VARS, which are only
finally available when all extensions' ext_localconf.php is included.

For this reason, Locales::initialize() can be deprecated
and moved into the regular constructor, but then the Bootstrap
should not do the initialization anymore, which happens
at the point now, when Locales first gets initialized (which
happens in Frontend within TSFE and PageRenderer and
in Backend within $LANG).

For this reason, it is removed from Bootstrap, where it was
first placed in TYPO3 4.6 when no proper bootstrap
set up was given.

Resolves: #88569
Releases: master
Change-Id: Ife2e248412c1b206abffcdd21df0d01e44834cea
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61046


Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>