[no squash] CAO 'node' visual

[sfan5]

implements #10722

To do

This PR is Ready for Review.

How to test

This code gives you a tool that duplicates an arbitrary node as entity:

minetest.register_entity("test2:cloned", {
	initial_properties = {
		physical = true,
		collide_with_objects = false,
		collisionbox = {-0.5, -0.5, -0.5, 0.5, 0.5, 0.5},
		static_save = false,
	},
})

minetest.register_tool("test2:clone_tool", {
	description = "Clone Node",
	inventory_image = "plus.png",
	liquids_pointable = true,

	on_use = function(itemstack, placer, pt)
		if placer == nil or pt == nil or pt.type ~= "node" then
			return
		end
		local pos = vector.offset(pt.under, 0, 1.25, 0)
		local entity = minetest.add_entity(pos, "test2:cloned")
		if entity then
			entity:set_properties({
				visual = "node",
				node = core.get_node(pt.under),
			})
		end
		return itemstack
	end,
})

And this one gives you a tool that can make any node fall:

core.register_tool(core.get_current_modname() .. ":fall_tool", {
	description = "Falling Tool",
	inventory_image = "end_icon.png^[transform3",
	liquids_pointable = true,

	on_use = function(itemstack, placer, pt)
		if placer == nil or pt == nil or pt.type ~= "node" then
			return
		end
		local node = core.get_node(pt.under)
		local def = core.registered_nodes[node.name]
		if def and def.drawtype ~= "airlike" then
			local was = def.groups.falling_node
			def.groups.falling_node = 1
			core.check_for_falling(pt.under)
			def.groups.falling_node = was
		end
		return itemstack
	end,
})

[kromka-chleba]

Is this going to support scale? (making the node bigger/smaller)
The origin point is going to be in the center of the node entity?

[sfan5]

It will support visual_size like anything else.

[lhofhansl]

Tried with random falling nodes and have observed no difference in behavior, with simpler code. Cool.