6544ea5035 refactor: Block unsafe fs::path std::string conversion calls (Russell Yanofsky)
b39a477ec6 refactor: Add fs::PathToString, fs::PathFromString, u8string, u8path functions (Russell Yanofsky)
Pull request description:
The `fs::path` class has a `std::string` constructor which will implicitly convert from strings. Implicit conversions like this are not great in general because they can hide complexity and inefficiencies in the code, but this case is especially bad, because after the transition from `boost::filesystem` to `std::filesystem` in #20744 the behavior of this constructor on windows will be more complicated and can mangle path strings. The `fs::path` class also has a `.string()` method which is inverse of the constructor and has the same problems.
Fix this by replacing the unsafe method calls with `PathToString` and `PathFromString` function calls, and by forbidding unsafe method calls in the future.
ACKs for top commit:
kiminuo:
ACK 6544ea5035
laanwj:
Code review ACK 6544ea5035
hebasto:
re-ACK 6544ea5035, only added `fsbridge_stem` test case, updated comment, and rebased since my [previous](https://github.com/bitcoin/bitcoin/pull/22937#pullrequestreview-765503126) review. Verified with the following command:
Tree-SHA512: c36324740eb4ee55151146626166c00d5ccc4b6f3df777e75c112bcb4d1db436c1d9cc8c29a1e7fb96051457d317961ab42e6c380c3be2771d135771b2b49fa0
1884ce2f4c