"Unified" release Qt source packages

For each release we create two sets of souce packages: Enterprise and Opensource. Unify those and simplify the release process.

Now the Enterprise src package prohibits configuring with "-opensource" and automatically defaults to "-enterprise". This needs to be changed in configure (qtbase/mkspecs/features/default_pre.prf) so that the unified src package accepts both "-opensource/-enterprise" options and based on the used option uses the license checker.

This also may need some cleaning/adjustments in CI/Coin what comes to patching of release source packages.

Configure configure functionality related to the license acceptance on the source package: https://intranet.qt.io/display/QTRD/Qt+configure+functionality+in+monolite+src+package
--> contains also suggestion for the unified source package functionality

Draft version of the unified specific release exporter: https://codereview.qt-project.org/#/c/190614
Draft version of the configure changes: https://codereview.qt-project.org/#/c/190643/