Switch to fmtlib
l10n: add plural forms data for Traditional Chinese (zh_TW)
download_and_compile.sh: add missing Qt deps and remove redundant CMake setting
download_and_compile.sh: remove old dependencies
download_and_compile.sh: switch from Qt 5 to Qt 6 (optional dependency)
WindowsMouseCursor: remove old disabled code that causes lupdate warnings
WindowsMouseCursor: remove old disabled code that causes lupdate warnings
CI: use the C.UTF-8 locale