QDS-13236 Update to Qt 6.8

This MR brings the following changes;

• chore: update to Qt6.8.0, EMSDK 3.1.56, and QtQuickDesigner Components to qds-dev-4.6-3-g20397e2
• cicd: support building for multithreaded and singlethread wasm binary
• enh: new window resizing method in C++

cicd/gitlab-ci.yml

 variables:
   # QT version and emsdk version must be compatible.
   # See https://doc.qt.io/qt-6/wasm.html
-  QDS_CI_QT_VERSION: "6.7.1"
-  QDS_CI_EMSDK_VERSION: "3.1.50"
+  QDS_CI_QT_VERSION: "6.8.0"
+  QDS_CI_EMSDK_VERSION: "3.1.56"
   QDS_CI_ARTIFACTS_PATH: "${CI_PROJECT_DIR}/artifacts"
   DEBIAN_FRONTEND: non-interactive
   GIT_SUBMODULE_STRATEGY: recursive