[BUGFIX] Load RequireJs in PageRenderer:: addRequireJsConfiguration()

``PageRenderer:: addRequireJsConfiguration`` does now load RequireJS
in the backend, as this method is called before ``loadRequireJs()``
otherwise, colliding with how ``loadRequireJs()`` handles RequireJS.

This is not done in frontend, as the output could get broken.

Resolves: #75353
Releases: master, 7.6
Change-Id: I7a1140036dcbf9ab869b361c40fedc3813a887d3
Reviewed-on: https://review.typo3.org/47478


Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Markus Sommer <markussom@posteo.de>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>