Make G_FILE_ATTRIBUTE_TIME_CREATED support stx_btime
With recent Linux kernels (>=4.15 ?), statx exposes the creation time of files.
Documentation says that G_FILE_ATTRIBUTE_TIME_CREATED corresponds to the NTFS ctime, but FreeBSD/NetBSD and some file systems other NTFS are also supported.
Users have asked us to expose this info on Thunar's UI, but instead of duplicating what Nemo devs did, I believe it's beneficial to the everyone to have this in GIO, just like KIO already has.