Add support for export_dmabuf_manager

[Babilinx]

After configuring wluma, i get an error saying that it is unable to init export_dmabuf_manager. It seems that Niri does not support this protocol and i think it will be nice if it does.

[YaLTeR]

Yeah we don't have that one. ...as, seemingly, no other compositor apart from sway?

Maybe it's more widely available in other wlroots compositors which are missing here?

[Babilinx]

I don't know at all. I just posted this because I see that it was missing. But it's not really an issue, just a comfort thing.