Currently, Flutter defaults to always using GTK
window decorations regardless of the window
manager, when running Wayland. This makes the app
look out of place on KDE Plasma and other Qt-based
desktop environments.
This change checks the XDG_CURRENT_DESKTOP
environment variable to determine the running
desktop environment, and if it is GNOME continues
to use the GTK header, otherwise it uses the Qt
header.
2f9ff47720