fix(core): avoid never type on iif when no else

[rodrigo1991]

Pull Request Template

PR Checklist

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
• I have added/updated documentation for any new behavior.
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]

PR Description

This pull request fixes the return types of iif not to force you to put a never third generic when not using elsePipeline

• no need to put a never third input type when we don't provide an else pipeline as the third parameter
  before:

iif<string, string, never>(
  (notEmptyString) => notEmptyString!==''
  () => 'the string is not empty'
)

now:

iif<string, string>(
  (notEmptyString) => notEmptyString!==''
  () => 'the string is not empty'
)

note that the this will not break the current code since the three parameters version of iif when not using elsePipeline will be marked as deprecated instead

[franher]

LGTM