Support large (> 2GB) files on windows.

This PR will use the functions _fseeki64() and _ftelli64() and struct stat64 on windows to ensure that files larger than 2GB are supported. The approach used is documented in : https://github.com/joakim-hove/ert/blob/9a108b30a7cbb35aa2bcd0f8c46e119230cebf87/devel/libert_util/src/util_lfs.c