Add Conditions to Thing Definitions or Creative Inventory Inclusion

[RonnymonnyTheProgrammer]

Some mods dynamically add/remove items based on configs and conditions; for instance, if a certain mod is loaded. It should also be possible to do this in thingpacks. Even if registry is mandatory, it should be possible to hide certain items from the creative tab and recipe mods.

[KnightMiner]

Neither Forge nor NeoForge support conditionally disabling registry entries based on config.

Considering other condition types, a mod loaded condition makes sense, but a condition on tags or alike does not as tags don't exist when Json Things loads things.

So I think the only actionable part of this request is considering a mod loaded condition.

---

Conditionally hiding contents from creative tabs makes sense to support as an alternative. Likely could be done as part of the creative tab JSON.

[KnightMiner]

Upon closer inspection, it seems Json Things already has conditions on most things. They are defined as an array "conditions": [ ... ] in most JSON objects.

There are two currently supported condition types:

• { "type": "mod_loaded", "modid": "some_value" }: conditions the object to a mod being loaded.
• { "type": "not", "condition": ... } inverts a condition.

I do think to call this fully resolved though, we probably should get an and and an or condition so we can properly nest logic.