Tests will now be built at `meson test`-time, so there's no cost if the
user isn't going to run them.
This is better than guarding on build type, as distros may want to test production
builds before shipping.
Signed-off-by: Sam James <sam@gentoo.org>
Adding meson build files for json-c that work similarly to the cmake build files.
Where it made sense, I reused existing cmake .h.in files or generated entirely from meson.
All tests were done with GCC and Clang in ubuntu 24.04, Windows using MSVC 2022 and Clang-cl from llvm's repo using version 21.1.3
Signed-off-by: Tyler Erickson <tyler.erickson@seagate.com>