The aim of this commit is to easily build qelectrotech under windows
with qt6/cmake and the package tool MSYS2.
-Update some cmake file.
-Remove Git submodule for pugixml and single application
-Use cmake find_package for pugi xml
-Use cmake fetchContent for single application.
-Use cmake find_package for KCoreAddons and KWidgetsAddons.
-Minor change for pugi xml
-Minor change on ProjectPrintWindow class to compatible with Qt6 API.
First build with qt6 and cmake.
QET compil, but a lot of things don't work.
Build tested on debian sid and ubuntu 25.04.
Dependency needed under debian and ubuntu :
qtcreator cmake qt6-tools-dev qt6-svg-dev libsqlite3-dev
libkf6coreaddons-dev extra-cmake-modules libkf6widgetsaddons-dev