DOS support (tracking issue)

What we need to nicely support DOS games

• Either enable overlay, switch to the directory portal, or use host:rw file permissions
• DOSBox-SVN doesn't support auto CPU cycles
• Enable dynarec in the core: https://github.com/libretro/dosbox-svn/pull/46
• Need to do something with shortcuts (#271 (moved))
• Enable retro-gtk mouse (and later keyboard) grab for DOS, provide a way to exit (probably similar to Boxes)
• Support keyboard grab: GNOME/retro-gtk#44
• Support mouse grab on Wayland: GNOME/retro-gtk#46
• Fix mouse grab so the the pointer doesn't escape the view: GNOME/retro-gtk#45
• The core is supposed to use hardware keycodes, but gets keyval instead: GNOME/retro-gtk!79