refactor: replace boost::filesystem with std::filesystem

Warning: Replacing fs::system_complete calls with fs::absolute calls
in this commit may cause minor changes in behaviour because fs::absolute
no longer strips trailing slashes; however these changes are believed to
be safe.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

src/qt/sendcoinsdialog.cpp

@@ -29,7 +29,10 @@
 #include <wallet/fees.h>
 #include <wallet/wallet.h>
 
+#include <array>
 #include <chrono>
+#include <fstream>
+#include <memory>
 
 #include <QFontMetrics>
 #include <QScrollBar>
@@ -509,7 +512,7 @@ void SendCoinsDialog::sendButtonClicked([[maybe_unused]] bool checked)
             if (filename.isEmpty()) {
                 return;
             }
-            fsbridge::ofstream out{filename.toLocal8Bit().data(), fsbridge::ofstream::out | fsbridge::ofstream::binary};
+            std::ofstream out{filename.toLocal8Bit().data(), std::ofstream::out | std::ofstream::binary};
             out << ssTx.str();
             out.close();
             Q_EMIT message(tr("PSBT saved"), "PSBT saved to disk", CClientUIInterface::MSG_INFORMATION);