fix(signals): add `StateSignal` to the public API

[ducin]

expose StateSignal store type in order to make it easier for 3rd party extensions to wrap signal store APIs, e.g. patchState with immer immutability - generic StateSignal<State> is difficult to obtain via ReturnType<typeof signalStore> or any other way.

no breaking changes

PR Checklist

Please check if your PR fulfills the following requirements:

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PR Type

What kind of change does this PR introduce?

[X] Refactoring (no functional changes, no api changes)

What is the current behavior?

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[X] No

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[rainerhahnekamp]

I think that one was already on the table: https://github.com/ngrx/platform/issues/4116#issuecomment-1803971396

[ducin]

@rainerhahnekamp not sure if that's the same thing - I don't care about the symbol.

Lacking the type is a blocker when it comes to providing a more specialized patchState. The original one is:

export declare function patchState<State extends object>(stateSignal: StateSignal<State>, ...updaters: Array<Partial<State & {}> | PartialStateUpdater<State & {}>>): void;

I just need to know the StateSignal type for the wrapping function; it's type-only, no effect on runtime whatsoever.

And I can't infer it, as it's generic :( type param gets inferred to object because of:

export type StateSignal<State extends object> = {
...
};

[rainerhahnekamp]

Ah, I see; I remember struggling with that object as well and giving up in the end.

[markostanimirovic]

Thanks Tomasz! Btw, public API exports are usually released as features. Since @ngrx/signals is still in the dev preview, I changed the PR type to fix, so it can be released in the patch release too.