Registering custom input kinds seems impossible

[Cedev]

Which feature is frustrating to use or confusing?

Registering custom input kinds with CentralInputStore seem impossible. It's documented to do so

/// This plugin is added by default by [`InputManagerPlugin`],
/// and will register all of the standard [`UserInput`]s.
///
/// To add more inputs, call [`CentralInputStore::register_input_kind`] during [`App`] setup.

pub struct CentralInputStorePlugin;

During App setup the CentralInputStore, once it's been created, will be inside a resource inside the world inside the app, but register_input_kind require a mutable reference to the app in order to add a system.

leafwing-input-manager/src/user_input/updating.rs

Lines 43 to 46 in 54a361b

	pub fn register_input_kind<I: UpdatableInput>(
	&mut self,
	kind: InputControlKind,
	app: &mut App,

This is impossible because you need to hold a mutable reference to the App and to the CentralInputStore which is inside of it at the same time, exactly a situation the rust borrow checker is designed to prevent.

Expectation

How do you intuitively expect this to behave?

Instead provide a method that takes the App, the control kind, and the UpdatableInput type, finds the CentralInputStore from the App, mutates its state as necessary and then adds the system to the App (while no longer holding a mutable reference to the CentralInputStore at the same time).

[alice-i-cecile]

This should be changed to only take a mutable reference to the app, and then fetch the CentralInputStore from the App.