Switch to C++20, RocksDB to 9.1.1, update docker images, GCC to 13.x, jemalloc to 5.3.0, and other misc fixups + bump version to 1.11.0

[cculianu]

This PR switches the C++ standard to C++20. As a part of this change, various things needed to be updated:

• RocksDB 6.x seemed to not like to compile with -std=c++20, so we updated to latest RocksDB 9.1.1
  • This brings with it a non-forward compatible change to the DB. If user uses 9.1.1 and then tries to go back to 6.x, Fulcrum will complain and exit.
  • In-tree binary images have all been updated to rocksdb 9.1.1
• Bumped Fulcrum version to 1.11.0 due to the above compatibility caveat.
• Updated docker images to use gcc 13.1 on Linux and gcc 13.2 on Windows.
• Removed support for Ubunu 16 (because we couldn't easily find a sufficiently new compiler for it).
• Updated Windows docker image to use latest mxe
• Bonus: Linux binaries now are statically linked to libstdc++, to maximize compatibility with stock systems.
• Updated jemalloc to 5.3.0 (previous had some warnings when compiling with gcc 13.x)
• Updated libzmq and cppzmq to latest (previous had warnings under latest gcc)
• Fixup to simdjson.hpp (had some C++20 warnings).
• Minimum Qt version is now 5.15.2 simply because I don't trust the earlier versions to work on with C++20.
• Misc other fixups (see commits).