[BUGFIX] Fix dependencies for non-composer extensions

The method packageRequirementIsComposerPackage of
TYPO3\CMS\Core\Package ignores all non composer package
names and thus dependency resolving of non composer packages
doesn't work.

This patch adapts the behavior to ignore just the platform
package links described here
http://getcomposer.org/doc/02-libraries.md#platform-packages

Fixes: #54142
Releases: 6.2
Change-Id: Idb6a837eebf792c6cbf9394885edc17c9d392a9f
Reviewed-on: https://review.typo3.org/26619
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader