Provide better version information in case we have found a non-matching QML module

CMake will print out the found version, which will help debugging. For example:

-- qmlplugindump failed for org.kde.kirigami.
-- Could NOT find org.kde.kirigami-QMLModule (missing: org.kde.kirigami-QMLModule_FOUND) (found version "1.123")

Also, move the qmlplugindump logic in one central place.