Checklist for Qt 6.0 inclusion

This document is still in draft mode.

Qt 6 will introduce a lot of changes when compared to Qt 5. To begin with, Qt 6 requires C++17 which by itself excludes some compiles which were supported as part of Qt 5. Other changes are related to APIs, the build system (move from qmake to cmake as Qt's internal build system) or general infrastructure changes in the CI and test infrastructure. Given the deadline for the Qt 6.0 release at the end of 2020, it is likely that not all Qt modules will be ready for the deadline set by the 6.0 release schedule. The intention of this page is to state and track the requirements that a Qt module needs to fulfill in order to be part of the Qt 6.0 release. If the release criteria is not met maintainers may choose to release their module with the next minor release in the 6.0 series.