Next Log4cxx Major release thoughts

[rm5248]

Whenever we do a new major release of Log4cxx(also breaking ABI compatibility), what should we do? My current thoughts are as follows:

1. Remove APR(or at the very minimum make it optional). I would like to see the core library be in just standard C++
2. What should the minimum C++ version be? C++20 includes std::source_location, while C++23 includes std::stacktrace
3. add constexpr to a bunch of functions? I've been reading up on how constexpr works, so perhaps some more thoughts on this later
4. Are there certain operations that could be better handled by newer C++ features? For example, could we make the API more usable by removing the LOG4CXX_DEBUG family of macros and instead use variadic templates?
5. Do we have any areas in the code where performance is a known problem, and could a redesign help to eliminate performance issues?
6. What about C++ modules? Are traditional headers ever going away?

Features to definitely keep:

1. Static declaration of loggers. While this does lead to undefined behavior at times(generally when exiting), being able to statically declare a logger is very important to me.

What other thoughts do people have?

In terms of timelines, I wouldn't expect a new version to be done before the end of 2026, so this is a pretty long timeline.