[refactor] Organize STRING

kernel/serial.cpp

@@ -1,5 +1,5 @@
 #include <serial.h>
-#include <common.h>
+#include <string_utils.h>
 
 extern EFI_SYSTEM_TABLE *ST;
 
@@ -22,7 +22,7 @@ void serial_write_char(char c) {
     }
 }
 
-void serial_write(const char *str) {
+void serial_write(String str) {
     if (!g_serial.SerialIo) {
         uefi_call_wrapper(ST->ConOut->OutputString, 2, ST->ConOut, (CHAR16*)L"serial: null io\n");
         return;