feat(component-store): add patchState method

[markostanimirovic]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/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?

// case 1
this.moviesStore.setState(state => ({
  ...state,
  movies,
}));

// case 2
this.moviesStore.setState(state => ({
  ...state,
  movies: [...state.movies, movie],
}));

Closes #2786

What is the new behavior?

// case 1
this.moviesStore.patchState({ movies });

// case 2
this.moviesStore.patchState(state => ({
  movies: [...state.movies, movie],
}));

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[ngrxbot]

Preview docs changes for 2c2fc55 at https://previews.ngrx.io/pr2788-2c2fc556/

[timdeschryver]

It keeps surprising (in a good way) me that this code "is so simple" 👍

[timdeschryver]

Should this test use the current state to build a new state?

e.g.

Suggested change

	componentStore.patchState(() => ({ value2: { foo: 'fooBar' } }));
	componentStore.patchState((state) => ({ value2: { foo: state.value2.foo + "2" } }));

[markostanimirovic]

sure 🙂

[alex-okrushko]

Thanks for working on this 👍

[alex-okrushko]

updater (and setState that calls the updater) does this check, so it's not needed here.

[markostanimirovic]

done

[alex-okrushko]

a few suggestions:

1. We can use this.setState here
2. Let's extract and evaluate patchedState separately for readability purposes.

Suggested change

	const updaterFn = (state: T) => ({
	this.setState((state) => {
	const patchedState = (typeof partialStateOrUpdaterFn === 'function')
	? partialStateOrUpdaterFn(state)
	: partialStateOrUpdaterFn;
	return {
	...state,
	...patchedState, // 👈 comes after `state` to override the properties
	};
	}

[markostanimirovic]

done