+ Check early for Qt6 and remove module list duplication.
+ Add qrencode-win32 as a submodule. Remove unused libqrencode
submodule(GNU/Linux and macOS use package dependencies).
+ Remove unused ReleaseCompile option.
REQUIRES adjustments to:
- https://jenkins.jami.net/view/clients/job/client-qt-msvc-tests
(JenkinsFile ??)
Gitlab: #601
Change-Id: Ied65c9aaead86009d70f68705f8592950dab2dfa