Merge bitcoin/bitcoin#33550: Fix windows libc++ fs::path fstream compile errors

c864a4c194 Simplify fs::path by dropping filename() and make_preferred() overloads (Ryan Ofsky)
b0113afd44 Fix windows libc++ fs::path fstream compile errors (Ryan Ofsky)

Pull request description:

  Drop support for passing `fs::path` directly to `std::ifstream` and `std::ofstream` constructors and `open()` functions, because as reported by hebasto in https://github.com/bitcoin/bitcoin/issues/33545, after https://wg21.link/lwg3430 there is no way this can continue to work in windows builds, and there are already compile errors compiling for windows with newer versions of libc++.

  Instead, add an `fs::path::std_path()` method that returns `std::filesystem::path` references and use it where needed.

ACKs for top commit:
  hebasto:
    ACK c864a4c194.
  l0rinc:
    Code review ACK c864a4c194
  maflcko:
    re-ACK c864a4c194 🌥

Tree-SHA512: d22372692ab86244e2b2caf4c5e9c9acbd9ba38df5411606b75e428474eabead152fc7ca1afe0bb0df6b818351211a70487e94b40a17b68db5aa757604a0ddf6

src/test/script_assets_tests.cpp

@@ -159,7 +159,7 @@ BOOST_AUTO_TEST_CASE(script_assets_test)
     bool exists = fs::exists(path);
     BOOST_WARN_MESSAGE(exists, "File $DIR_UNIT_TEST_DATA/script_assets_test.json not found, skipping script_assets_test");
     if (!exists) return;
-    std::ifstream file{path};
+    std::ifstream file{path.std_path()};
     BOOST_CHECK(file.is_open());
     file.seekg(0, std::ios::end);
     size_t length = file.tellg();