LibCore: Add Directory::chown() API and use it in Core::Account

Since we already have the directory open, let's have an API to fchown()
the underlying file descriptor instead of forcing clients to do another
path lookup.

Userland/Libraries/LibCore/Account.cpp

@@ -152,8 +152,8 @@ bool Account::authenticate(SecretString const& password) const
 ErrorOr<void> Account::create_user_temporary_directory_if_needed() const
 {
     auto const temporary_directory = String::formatted("/tmp/user/{}", m_uid);
-    TRY(Core::Directory::create(temporary_directory, Core::Directory::CreateDirectories::Yes));
-    TRY(Core::System::chown(temporary_directory, m_uid, m_gid));
+    auto directory = TRY(Core::Directory::create(temporary_directory, Core::Directory::CreateDirectories::Yes));
+    TRY(directory.chown(m_uid, m_gid));
     return {};
 }
 

Userland/Libraries/LibCore/Directory.cpp

@@ -31,6 +31,14 @@ Directory::~Directory()
         MUST(System::close(m_directory_fd));
 }
 
+ErrorOr<void> Directory::chown(uid_t uid, gid_t gid)
+{
+    if (m_directory_fd == -1)
+        return Error::from_syscall("fchown"sv, -EBADF);
+    TRY(Core::System::fchown(m_directory_fd, uid, gid));
+    return {};
+}
+
 ErrorOr<bool> Directory::is_valid_directory(int fd)
 {
     auto stat = TRY(System::fstat(fd));

Userland/Libraries/LibCore/Directory.h

@@ -43,6 +43,8 @@ public:
 
     ErrorOr<LexicalPath> path() const;
 
+    ErrorOr<void> chown(uid_t, gid_t);
+
     static ErrorOr<bool> is_valid_directory(int fd);
 
 private: