feat(signals): add signalStore and signalStoreFeature

[markostanimirovic]

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• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #4000

What is the new behavior?

signalStore and signalStoreFeature functions are added to the @ngrx/signals package.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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[brandonroberts]

[timdeschryver]

I like the different files for each feature 🤩
As mentioned earlier, it seems like my WebStorm fails to infer some types, while VSCode can.

[timdeschryver]

Does this generic has a meaning?

Suggested change

	function withCustomFeatureWithInput<_>() {
	function withCustomFeatureWithInput() {

[markostanimirovic]

I noticed a weird typing bug when custom features with input are used in complex use cases.

Here is the reproduction. If we remove <_> from withY, the compilation error will be thrown in SignalStores that use withY feature although the generic isn't used anywhere. 👀

This is a rare case, but I'll document this behavior and there will be a recommendation in the docs.

[timdeschryver]

I got a question about the usage of type.
If I understand this correctly, the type is used here to make the store typesafe? In this case, this feature expects that it's used within a store that has a foo state property, and a s signal property.

[markostanimirovic]

Exactly!

[timdeschryver]

Congrats on closing #4000! 🚀

[Maciejlys]

When can we expect release of this? I assume this will be a npm package ngrx/signals?