[BUGFIX] setSingletonInstance should respect XCLASS registrations

GeneralUtility::makeInstance() stores singleton instances in their
overridden class names, however, when using setSingletonInstance
(which is used in TSFE) this is not connected, making a setSingletonInstance
break with another makeInstance call afterwards - returning a new,
non XCLASSED object.

Resolves: #73671
Resolves: #80399
Releases: master, 9.5
Change-Id: Ibb0005575db3fec55149a0624929c941c1491ed8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63618


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>