invoke fixes:

[CaseyCarter]

• "default" coerce overload needs to be SFINAE-friendly
• Use is_base_of instead of derived_from per [func.require]
• reference_wrapper and is_base_of overloads of coerce are unconditionally noexcept
• Don't check is_function_v/is_object in PMF/PMD invoke overloads when we can simple check the validity of the result expression
• Implement invoke_result in terms of invoke_result_t
• Avoid declval in reference_wrapper::operator()