[tools] Add wallet inspection and modification tool

Summary:
This commit adds wallet-tool, a tool for creating and interacting with
wallet files. Original implementation was by Jonas Schnelli
<dev@jonasschnelli.ch> with modifications by John Newbery
<john@johnnewbery.com>

• [tests] Add wallet-tool test

Original tests by João Barbosa <joao.paulo.barbosa@gmail.com>

Additional contribution by John Newbery <john@johnnewbery.com>

This is a backport of Core PR13926

Depends on D5749 and D5750

Test Plan:

./test/functional/test_runner.py tool_wallet.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5751