feat(signals): provide support for scoped events

[markostanimirovic]

PR Checklist

Please check if your PR fulfills the following requirements:

• 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 #4776

What is the new behavior?

// === providing scoped dispatcher: ===
{ providers: [provideDispatcher()] }

// === dispatching events to the parent/global scope: ===
// scope values: 'self' | 'parent' | 'global' ('self' by default)

const event1 = event('event1');
const event2 = event('event2');

// using Dispatcher:
const dispatcher = inject(Dispatcher);
dispatcher.dispatch(event1(), { scope: 'parent' });

// using injectDispatch:
const dispatch = injectDispatch({ event1 });
dispatch({ scope: 'global' }).event1();

// using toScope:
withEffects((_, events = inject(Events)) => ({
  $: events.on(event1).pipe(
    map(() => [event2(), toScope({ 'parent' })]),
  ),
}))

// using mapToScope:
withEffects((_, events = inject(Events)) => ({
  $: events.on(event1).pipe(
    map(() => event2()),
    mapToScope('global'),
  ),
}))

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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[rainerhahnekamp]

Will you provide the updated documentation in a separate PR?

[markostanimirovic]

@rainerhahnekamp Yes, I'll add a new section 'Scoped Events' without changing existing content from the Events page because the previous behavior remained the same.

[rainerhahnekamp]

That is important for the event tracker in the toolkit. 👍

[rainerhahnekamp]

LGTM 👍

[timdeschryver]

Lovely! 🤩