[wallet] Add CWallet::Verify function
Summary:
This allows a single wallet to be verified. Prior to this commit, all wallets were verified together by the WalletInit::Verify() function at start-up. Individual wallet verification will be done when loading wallets dynamically at runtime.
Partial backport of core PR10740 (commit e0e90db)
https://github.com/bitcoin/bitcoin/pull/10740/commits/e0e90db07b4e798dd1625bd23c2e9bd96fc6ff49
Progress towards T459
Depends on D3631
Test Plan:
make check ./test/functional/test_runner.py wallet_*
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D3632