Add console output codepage for windows (#967)

Previously unicode codepoints would be incorrectly shown in windows
terminals, such as with u2503(┃):
```ps
❯ "print('\u{2503}')" | luau.exe
Γöâ
```

This change fixes the issue by setting the console's codepage on
windows, resulting in fixed behaviour:
```ps
❯ "print('\u{2503}')" | luau.exe
┃
```

CLI/Repl.cpp

@@ -675,6 +675,10 @@ int replMain(int argc, char** argv)
 
     setLuauFlagsDefault();
 
+#ifdef _WIN32
+    SetConsoleOutputCP(CP_UTF8);
+#endif
+
     int profile = 0;
     bool coverage = false;
     bool interactive = false;