Refactor: use one common function to resolve callable objects

[hirotasoshu]

Is your feature request related to a problem? Please describe.
At the moment there is duplicate code in many places that resolves callable objects from string path or object itselfs and it would be nice to clean that up

Describe the solution you'd like
Create one common function to resolve callable objects

Describe alternatives you've considered
None

Additional context
Proposed by @aleksihakli in #1058 (comment)

[aleksihakli]

This would be a nice update to clean up the current code, and possibly to reduce the required unit test scope as well. Refactoring the resolvers could possibly enable refactoring the tests a bit in the same go. Could maybe be good to refactor the current resolvers first, and maybe open a separate PR on the test refactoring afterwards, if needed?