Rework state checkpoint enum handling

Rework state checkpoint enum handling

The state enumerations have been changed to enum classes and enumeration
arrays. This was required by clang-tidy to remove the global available char
arrays.

Added templated function to convert enum to underlying int.

Was able to simplify quite a lot of the checkpoint handling that had to
work around the pure ints used before the enumerations to get the
correct names for the entries.