NodeGroup Add generic type from incoming data

[FranzFlueckiger]

This PR allows typescript users to directly have the type of the incoming data array inferred in all the following functions:
keyAccessor, start, enter, update and leave.
If this PR is accepted, nothing will change from the user's perspective except that they will enjoy code completion where they might expect it to be.

[sghall]

Good point 👍 Keep thinking I'm just going to re-write this in TS. I think you need to make it optional, right? So not all TS users need to provide a type?

Like...

type SomeType<T = void> = OtherType<T>;

https://garbagevalue.com/blog/optional-generic-typescript

[FranzFlueckiger]

Hi Steve, sorry for the late response. You're right that the generic should be optional so that this change is non-breaking for the users.

[haydn]

I feel like it's just as important to tighten-up the any type here too. I've got this type in my codebase:

type ReactMoveNode<Data, State> = {
  key: string;
  data: Data;
  state: State;
};

That I'm using like this:

<NodeGroup
 // ...etc
>
  {(
    nodes: Array<ReactMoveNode<{ id: string }, { top: number; opacity: number }>>
  ) => (
    // ...etc
  )}
</NodeGroup>

It should be possible to wrap all that up together here.