Added a script to generate chainparams constants from intermediate files
Building on D3732 so that chainparams constants no longer need to be copy-pasted manually.
Depends on D4140
For actually testing the process flow, generate the chainparams_*.txt files:
bitcoind make_chainparams.py > chainparams_main.txt bitcoind --testnet make_chainparams.py -a 127.0.0.1:18332 > chainparams_main.txt
For this diff, I did not do the above, I copied the existing chainparams manually into the chainparams_*.txt files so that we don't add updating those to the review process of this diff.
After the chainparams_*.txt files are ready, do the following:
generate_chainparams_constants.py . make check ninja check
Reviewers: #bitcoin_abc, deadalnix, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D4120