GetCPInfoExA() is missing on some Windows platforms, load it dynamically.
- ConvertINetMultiByteToUnicode/ConvertINetUnicodeToMultiByte should return required target length if the target buffer is NULL - add the tests for all the above - fix IMultiLanguage2 vtable (it was missing ConvertStringFromUnicodeEx)
Added an implementation of mlang.dll and test cases for it.