feat(effect): catch action creators being returned in effect without ()

[alex-okrushko]

PR Checklist

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• 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?

In #2306 we are catching actionCreators that are not called in store.dispatch(actionCreatorNotCalled) at compile time, however it was still possible to map to ActionCreator in the effects by accident: https://twitter.com/DeborahKurata/status/1263612553067819008

[ ] 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?

We are catching at runtime, which is nice, but we can do better.

Closes #

What is the new behavior?

Catch ActionCreators that are not called at compile time:

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Well... somewhat. I needed to adjust the error message and throwError operators (or any other one that returns never) would not be taken any more.

Other information

[ngrxbot]

Preview docs changes for 89b509f at https://previews.ngrx.io/pr2536-89b509f/

[timdeschryver]

Great!