[BUGFIX] Set locale for FormatSize

As LC_NUMERIC is not set via Locales::setLocale
because conflicts on float calculation may occur,
we have to manually set LC_NUMERIC in places where
we need the locale aware numeric functionality.

In the core this is only formatSize - which missed
the LC_NUMERIC handling since the switch to
SiteConfiguration. With this patch, the handling is
reintroduced by using the locale set by setLocale for
LC_MONETARY to temporarily set LC_NUMERIC in formatSize.

Resolves: #101211
Releases: main, 12.4
Change-Id: Id694f04fb07fb421644fa87c415d786ca11bcfaa
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79592


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>