> Following the main.cpp split, there are still some constants in the wrong places, eg net_processing constants in validation.h. Move them all to their rightful homes. At the same time, make them constexpr.
>
> Also move all const declarations to the top of their files, and ensure that they all have doxygen comments.
This is a backport of Core PR17383 [1/4]
https://github.com/bitcoin/bitcoin/pull/17383/commits/b8580cacc70764ba5a48e3defb864d75e6c28626