Use fmt lib for complicated string formatting

[abeltrano]

Is your feature request related to a problem? Please describe.
The text formatting updates to C++ 20 require specifying non-standard options (clang) and/or very new compiler versions (g++, clang). Since we'd like to keep the build environment simple, we don't want to take this route. It'd be nice to simplify complicated string formatting with std::format like functionality in a library that supports reasonable versions of MSVC, clang, and g++.

Describe the solution you'd like
The fmt library is one solution that satisfies the above criteria. Unfortunately it's not a drop-in replacement for std::format, so would require some rework to switch to the standard implementation if it becomes more widely available in the medium term.