Use std::invoke_result_t instead of deprecated/removed std::result_of

[adayton1]

Summary

• This PR is a bugfix
• It does the following:
  • std::result_of was deprecated in C++17 and removed in C++20
  • Uses std::invoke_result_t instead
  • Handles the first case in issue C++20 support #1718.

[kennyweiss]

Thanks @adayton1 !

[Arlie-Capps]

Thank you, @adayton1 !

[rhornung67]

@adayton1 did you say earlier that there are similar changes needed to some other files?

[adayton1]

@adayton1 did you say earlier that there are similar changes needed to some other files?

#1718

• CLI11.hpp, but I think it is correctly guarded with macros.
• sol.hpp, but I don't feel comfortable trying to mess with that library.

[adayton1]

I do not have permissions to merge, so feel free to push the button @kennyweiss or @rhornung67.