[BUGFIX] Enable Enhancer support for MountPoints

When using e.g. PageTypeDecorator in conjunction with mountpoints
and other Enhancers, the MP parameter was not added to the
resulting PageArguments object.

In addition, when building up a RouteCollection internally, the
same page was used multiple times but was overridden with a
MountPoint argument, adding to the "last principle wins" concept.

The patch adapts the needed changes.

Resolves: #90731
Releases: master, 9.5
Change-Id: Ic8c70dd51dc37617ba97cace3b9bec63512ecad6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64403


Tested-by: Jan Kornblum <jan.kornblum@gmx.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Jan Kornblum <jan.kornblum@gmx.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>