feat(spectator): support for Function-based outputs

[anatolie-darii]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngneat/spectator/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have 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?

currently there are a couple of issues with spectator.output

1. Unless you add a specific return type then it returns an Observable<unknown>
2. Doesn't support function based outputs (https://angular.dev/guide/components/output-fn#)

What is the new behavior?

1. Added 2 additional overloads for the output method

• one very similar to the existing one but with the return type OutputEmitterRef<T>
• one that infers the return type based on the key name.

2. Limit the output names at compile time to field names that are of an output type

Does this PR introduce a breaking change?

[ ] Yes
[x] No

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