Use std::common_type_t to compare variables using common type

[leekillough]

Use std::common_type_t to simplify the comparison of different variable types. If a common type exists for which both operands can be explicitly converted to, then you convert them to this common type and perform the comparison on this common type.

• Note: std::common_type_t<std::bitset<N>::reference, bool> = bool and std::common_type_t<std::vector<bool>::reference, bool> = bool.
• std::common_type<T1, T2> is the only <type_traits> class which can have user-defined specializations, as long as at least T1 or T2 is a user-defined type, but I did not need to define a specialization.

Use the same cmp() function which uses std::common_type_t for both variable change-detection as well as regular comparisons.

[github-actions]

CLANG-FORMAT TEST - PASSED

[sst-autotester]

Status Flag 'Pre-Test Inspection' - - This Pull Request Requires Inspection... The code must be inspected by a member of the Team before Testing/Merging
NO INSPECTION HAS BEEN PERFORMED ON THIS PULL REQUEST! - This PR must be inspected by setting label 'AT: PRE-TEST INSPECTED'.