fs: consistently use fsbridge for {i,o}fstream

Part of #20744, but this can be done now, and will simplify the diff.

src/qt/walletframe.cpp

@@ -210,7 +210,7 @@ void WalletFrame::gotoLoadPSBT(bool from_clipboard)
             Q_EMIT message(tr("Error"), tr("PSBT file must be smaller than 100 MiB"), CClientUIInterface::MSG_ERROR);
             return;
         }
-        std::ifstream in(filename.toLocal8Bit().data(), std::ios::binary);
+        fsbridge::ifstream in{filename.toLocal8Bit().data(), std::ios::binary};
         data = std::string(std::istreambuf_iterator<char>{in}, {});
     }