Add runtime access to SpacePlatformStarterPackPrototype.trigger

[ignatio]

What?

See title.

Why?

It's useful to determine how space-platform-hub entities are created. I'd like to use that info in a mod that extracts data for a calculator tool.

(Apologies if this exists already and I simply missed it. I expected to find it as LuaItemPrototype.trigger, or some field in that class with TriggerItem in the type.)

[Koub]

[Koub] Moved to Modding interface requests.

[Bilka]

This was added as LuaItemPrototype::trigger.