Make clay oven more moddable

[Craluminum2413]

Don't hardcode contents model (ovenFuelShape), get ovenFuelShape from collectible attributes of containing item instead.

In this example I made peat brick a suitable fuel for clay oven. by adding this to attributes in blocktypes/soil/peatbrick.json:

isClayOvenFuel: true,
ovenFuelShape: "block/peatbrick",

and this to textures:

"0": {base: "block/soil/peat"},

[Craluminum2413]

Strange, it somehow changed entire file

[Craluminum2413]

Oh this is why

So basically all I do is changing this line:

var loc = AssetLocation.Create(Block.Attributes["ovenFuelShape"].AsString(), Block.Code.Domain).WithPathPrefixOnce("shapes/").WithPathAppendixOnce(".json");

to these lines:

string shapeLoc = this.Block.Attributes["ovenFuelShape"].AsString();
if (this.FuelSlot?.Itemstack?.Collectible.Attributes.KeyExists("ovenFuelShape") == true)
{
    shapeLoc = this.FuelSlot.Itemstack.Collectible.Attributes["ovenFuelShape"].AsString();
}

var loc = AssetLocation.Create(shapeLoc, Block.Code.Domain).WithPathPrefixOnce("shapes/").WithPathAppendixOnce(".json");

[Craluminum2413]

Fixes anegostudios/VintageStory-Issues#2563