Allow wallet files in multiple directories
Summary:
Remove requirement that two wallet files can only be opened at the same time if they are contained in the same directory. This change mostly consists of updates to function signatures (updating functions to take fs::path arguments, instead of combinations of strings, fs::path, and CDBEnv / CWalletDBWrapper arguments).
Partial backport of core PR11687 (commit d8a99f6)
https://github.com/bitcoin/bitcoin/pull/11687/commits/d8a99f65e53019becdd8d2631396012bafb29741#diff-5ddca6879fe54b576a2fc4598d9f29ce
Depends on D3102
Progress towards T651
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/D3103