graphics/wayland-protocols: update to 1.20

Changes: https://lists.freedesktop.org/archives/wayland-devel/2020-February/041267.html
Changes: https://lists.freedesktop.org/archives/wayland-devel/2020-February/041269.html
PR: 244583
Approved by: manu, imp, zeising (x11)
Differential Revision: https://reviews.freebsd.org/D23906