Refactor the code

[plfiorini]

• [x] Remove client code
• [x] Remove deprecated code
• [x] Remove all qmake traces and use our CMake functions.
• [x] Rename qtwaylandscanner
• [x] Remove QT_(BEGIN|END)_NAMESPACE macros
• [x] Cherry-pick Qt 6 changes
• [x] Check all QT_DEPRECATED_SINCE
• [x] Check all Qt version checks
• [x] Rename logging categories
• [x] Namespaces
• [x] Fix buffer integration path
• [x] Replace QtWayland feature macros (QT_CONFIG, QT_REQUIRE_CONFIG, QTFEATURE*)
• [x] Rename classes to remove references to Qt
• [x] Rename files to reflect class names
• [x] Import QtXkbCommonSupport code