Add birthtime to file node layout for file creation time

[humphd]

Our filenode layout includes atime, mtime, and ctime. We don't have birthtime. See https://nodejs.org/api/fs.html#fs_stat_time_values. We'd also need to add this to Stats as birthtime and birthtimeMs.

This would be a breaking change, requiring us to substitute something like ctime in older versions of a filesystem.

[andrewkoung]

@humphd I'm currently analyzing this issue out of interest if you don't mind cause maybe I'll understand the purpose of the project since I still don't. I took a look into the node.js and stats.js files though since they seemed to be the place where the additions will happen, but wanted to know the significance of these files.

[humphd]

The idea of this would be that when we create a file node, in addition to setting the atime, mtime, and ctime, we'd also add birthtime and it would never change.