[BUGIFX] Allow overriding system extensions

When making a copy of a system extension and place the copy
in typo3conf/ext, the package manager is capable of loading the copy
instead of the original extension. However the path of the classes would
still be wrong.

To support this feature properly, we need to create class maps of the
new location to override the already registered maps.

For this to work the package type needs to be changed
from "typo3-cms-framework" to "typo3-cms-extension" in composer.json of
the copied system extension.

Resolves: #70077
Releases: master
Change-Id: I77168b8957e7b5658ce710f13dedf258474b040b
Reviewed-on: http://review.typo3.org/43522


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>