[bugfix] wallet: Fix duplicate fileid detection

Summary:
```
The implementation in current master can not detect if the file ID is
duplicate with flushed BerkeleyEnvironment. This PR would store the file
ID in a global variable g_fileids and release it when the
BerkeleyDatabase close. So it won't have to rely on a Db*.
```

Depends on D4884.

Backport of core PR14320:
https://github.com/bitcoin/bitcoin/pull/14320/files

Test Plan:
  ninja all check
  ./test/functional/test_runner.py wallet_*

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4885