feat(effects): add mapToAction operator

[alex-okrushko]

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?

Introduces mapToAction operator that can take either the config object, or 2 parameters: project and error.

config has the following interface:

/** Represents config with named paratemeters for mapToAction */
export interface MapToActionConfig<
  InputAction extends Action,
  OutputAction extends Action,
  ErrorAction extends Action,
  CompleteAction extends Action,
  UnsubscribeAction extends Action
> {
  // Project function that produces the output actions in success cases
  project: (action: InputAction, index: number) => Observable<OutputAction>;
  // Error handle function for project
  error: (error: any, action: InputAction) => ErrorAction;
  // Optional complete action provider
  // count is the number of actions project emitted before completion
  // action is the action that was completed
  complete?: (count: number, action: InputAction) => CompleteAction;
  // Optional flattening operator
  operator?: <InputAction, OutputAction>(
    project: (input: InputAction, index: number) => Observable<OutputAction>
  ) => OperatorFunction<InputAction, OutputAction>;
  // Optional unsubscribe action provider
  // count is the number of actions project emitted before unsubscribing
  // action is the action that was unsubscribed from
  unsubscribe?: (count: number, action: InputAction) => UnsubscribeAction;
}

[ ] 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 # #1224

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[ngrxbot]

Preview docs changes for 29e89c6 at https://previews.ngrx.io/pr1822-29e89c6/

[alex-okrushko]

Waiting for #1795 to be merged, so I can adjust the path of NotificationKind - removing it from internal.

[ngrxbot]

Preview docs changes for 388ca02 at https://previews.ngrx.io/pr1822-388ca02/

[ngrxbot]

Preview docs changes for 96654cf at https://previews.ngrx.io/pr1822-96654cf/

[ThomasBurleson]

@alex-okrushko - should this include a README or docs on (a) Benefits and (b) How to use it ?

[ngrxbot]

Preview docs changes for 946f828 at https://previews.ngrx.io/pr1822-946f828/

[alex-okrushko]

FYI, I'm adding docs for this PR ATM.

[ngrxbot]

Preview docs changes for 43cba13 at https://previews.ngrx.io/pr1822-43cba13/

[timdeschryver]

Feedback on the docs

[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[ngrxbot]

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[timdeschryver]

👍