https://github.com/tcbrindle/span
Replacing a homebrew const pointer wrapper const correctness helper
with the C++20 like span library.
One day when we switch to C++20 we will just use the C++20 spans instead.
Reworked the FFF testing framework & ConfigBase::set_deserialize()
for more compact tests: set_deserialize() now accepts list
of key / value pairs.
Fixed an incorrect assert in LayerRegion.