What problem does this solve or what need does it fill?

I would like to be able to get or create a ComponentId with just TypeId (and TypeRegistry) assuming a given type reflects the required trait. This currently can only be done if a given component/resource has already been initialized (with Components::get_id and Components::get_resource_id).

A specific example: a scripting language that wants to check for existance of a resource/component (on an entity) where the resource resource/component is defined in rust.

What solution would you like?

For ReflectComponent:

• add a new function that takes &mut World and calls world.init_component::<T>()

For ReflectResource:

• would require adding a new method to World that initializes a resource without inserting
  • NOTE: based on current naming convention this should be called init_resource which is already used. Rename init_component and init_component_with_desciptor #15451 proposes a rename of this group of methods. This would mean the new method would be called register_resource<T>
  • NOTE: this is different than Add init_resource_with_descriptor #15448 as this method should return the same ComponentId for the same type if called multiple times
• add a new function that takes &mut World and calls this new function

What alternative(s) have you considered?

• Require users to manually register all resources/components they are planning to use first (this is what I'm currently doing)
• Somehow initialize all registered types that #[reflect(Component, Resource)] automatically when registering a type inside of the type registry.