wayland: Send accurate capabilities

mutter now knows whether the app menu should be shown, so expose this
properly under Wayland as well.
Support for hardware cursor sizes other than 64x64 on wayland

Use the new DRM capabilities to figure out the correct cursor size, and
make sure that matches instead of hardcoding 64x64. This fixes incorrect
rendering on some newer AMD cards that support 256x256 cursors.

Based heavily on a patch by:
Alvaro Fernando García <alvarofernandogarcia@gmail.com>