[BUGFIX] Normalize Windows file path in CompositeExpression

The path to the calling file in CompositeExpression::add and
::addMultiple is now normalized to forward slashes to work
with Windows paths.

Resolves: #99509
Releases: main
Change-Id: Ib00a541ee08343d9483b1474590dcd80f819723a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77321


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>