fileinfo: implement os_fileinfo_size

this replaces os_get_file_size and file_info.stat.st_size
fileinfo: implement os_fileinfo_hardlinks
fileinfo: implement os_fileinfo_blocksize
fileinfo: rename os_get_file_info{,_link,_fd}
fileinfo: rename os_file_info_id_equal
fileinfo: rename os_file_info_get_id
fileinfo: rename os_file_info_get_inode
fileid: rename os_get_file_id
fileid: rename os_file_id_equal
fileid: rename os_file_id_equal_file_info
fileinfo: change returntype of os_fileinfo_size

off_t -> uint64_t
Merge pull request #1054 from stefan991/fileinfo-getter

FileInfo getters for `filesize`, `hardlinks` and `blocksize`