Fix Windows locale problem

[ken2812221]

Fixes #13103
This PR make internal strings of Windows always be utf8-encoded

• Add UTF8 <-> localized string conversion function
• Use localized string on Berkeley DB
• Use localized string on LevelDB
• Use localized string on fstream::open
• Use std::fstream instead of fs::fstream

Patched the boost library to convert fs::path::string() to be UTF8 encoded. Add two functions that convert between UTF8 and Local encodes.

To those who want to test this, adding -datadir=(some non-ASCII characters) option make every file that Bitcoin Core use contain non-ASCII characters

Defect: If the user's codepage does not support the filename, it will be encoded to ?
I don't known how to solve this. Leveldb and Berkeley DB don't support wide char.

[laanwj]

maybe move to utilstrencodings?

[laanwj]

Thanks. Though I'm sad that this is needed.
To stay sane, and keep locales and encodings out of everything as much as possible:

• Please keep all our internal state in UTF-8 everywhere. This was always the intent, so in interaction with JSONRPC we can assume all strings are UTF-8, and matches with Qt's view.
• Only convert to local encoding when needed, so just before going to the file system layer, or when coming from the file system layer (or filenames, command-line arguments etc).

BTW, there are GUIUtil::qstringToBoostPath and GUIUtil::qstringToBoostPath to convert Qt strings from/to local paths but I don't think they are useful in this case as it doesn't happen on the interface from Qt to core code.

[ken2812221]

prefer #13426