Add scripts to dumpwallet RPC

Summary:
Adds the CScripts from the wallet to the dumpwallet RPC, includes a basic test, and modifies the helptext of the dumpwallet RPC.

This does not break importwallet, but the scripts are not imported yet.

Partial backport of core PR11667
commits cdc260a, b702ae8, 9e1184d, part of 1bab9b2 and 656fde5

Depends on D2415

Test Plan:

./test/functional/test_runner.py wallet_dump

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2416