LibCore: Use ErrorOr<T> for Core::File::open()

Userland/Utilities/arp.cpp

@@ -16,6 +16,7 @@
 #include <net/if_arp.h>
 #include <net/route.h>
 #include <netinet/in.h>
+#include <string.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
 #include <unistd.h>

Userland/Utilities/cksum.cpp

@@ -8,6 +8,7 @@
 #include <LibCore/File.h>
 #include <LibCrypto/Checksum/Adler32.h>
 #include <LibCrypto/Checksum/CRC32.h>
+#include <string.h>
 
 int main(int argc, char** argv)
 {

Userland/Utilities/errno.cpp

@@ -5,7 +5,7 @@
  */
 
 #include <LibCore/ArgsParser.h>
-#include <LibCore/File.h>
+#include <string.h>
 
 int main(int argc, char** argv)
 {

Userland/Utilities/hexdump.cpp

@@ -8,6 +8,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <ctype.h>
+#include <string.h>
 
 static constexpr size_t LINE_LENGTH_BYTES = 16;
 

Userland/Utilities/mv.cpp

@@ -9,6 +9,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/File.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/stat.h>
 #include <unistd.h>
 

Userland/Utilities/sql.cpp

@@ -178,7 +178,7 @@ private:
             auto file_name = m_input_file_chain.take_first();
             auto file_or_error = Core::File::open(file_name, Core::OpenMode::ReadOnly);
             if (file_or_error.is_error()) {
-                warnln("Input file {} could not be opened: {}", file_name, file_or_error.error().string());
+                warnln("Input file {} could not be opened: {}", file_name, file_or_error.error());
                 return {};
             }
             m_input_file = file_or_error.value();