[validation] Move all const declarations to top of validation.h
Summary:
This is a backport of Core PR17383 [3/4]
https://github.com/bitcoin/bitcoin/pull/17383/commits/507b36dd1bf867cd20e4312b95c68b494c9bb7b8
Depends on D8977
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D8978