GuiAnchor support for ghosts

[Quezler]

When GuiAnchor was implemented ghost guis weren't a thing yet.

When you use name or names as a filter it'll stop appearing on ghosts even if they share the name, which would require the player to just listen to the gui opened event of that gui type in general and then manually toggling it, which is not quite nice.

It would be nice if the relative gui when filtered by name would also open for entity ghosts matching the type & name defined in the filter.

For backwards compatibility with mods that do not expect the gui to open for their ghosts i would suggest an "include_ghosts = true" opt-in or something.

[Rseding91]

I've added ghost_mode to LuaGuiElement::anchor for the next release.