fix: don't create native messaging manifest file unless browser directory exists (#6116)

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/singletons/NativeMessaging.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "common/Atomic.hpp"
+#include "util/Expected.hpp"
 
 #include <QString>
 #include <QThread>
@@ -8,6 +9,19 @@
 #include <optional>
 #include <vector>
 
+namespace chatterino::nm::detail {
+
+enum class WriteManifestError : std::uint8_t {
+    FailedToCreateDirectory,
+    FailedToCreateFile,
+};
+
+nonstd::expected<void, WriteManifestError> writeManifestTo(
+    QString directory, const QString &nmDirectory, const QString &filename,
+    const QJsonDocument &json);
+
+}  // namespace chatterino::nm::detail
+
 namespace chatterino {
 
 class Application;