A function to get all entity identifiers, a function to get item identifiers, a function for particles...
system.getEntityIdentifiers() // ["minecraft:skeleton", "minecraft:zombie", ..., "my_namecpace:my_custom_entity", ...]
system.getItemIdentifiers() // ["wooden_sword", "stone_sword", "wooden_pickaxe", ...]
// similiar functions for other things
An alternative would be a single function which takes identifier type as parameter.
Example use case: A plugin which let's the player choose an entity type from a list to e. g. spawn it
