Port to GTK4 + libadwaita + gtk4-rs
This commit upgrades our rust dependencies and ports Tour to libadwaita+GTK4. As part of porting we now use GtkPicture instead of GtkImage, and AdwClamps to hold pages in place.
This commit upgrades our rust dependencies and ports Tour to libadwaita+GTK4. As part of porting we now use GtkPicture instead of GtkImage, and AdwClamps to hold pages in place.