Improve wl_pointer::set_cursor documentation regarding surface format
I propose to update wl_pointer::set_cursor documentation to indicate that the input surface should be alpha-premultiplied, that is, the R, G and B components should be already multiplied by their corresponding alpha.
As it is not always clear in X11 documentation, Xorg server now has a workaround when a client sets a new cursor with wrong data (non-alpha-premultiplied). For Wayland, I think it is not too late to inform developers how they should format their surface before calling that function.
This proposition comes after a discussion regarding a mouse cursor rendering problem with Xorg/amdgpu: https://bugs.freedesktop.org/show_bug.cgi?id=108355