Mark FileSystemFlags as standard (#5404)
Mark FileSystemFlags as standard (#5404)

`FileSystemFlags` is a standard part of the _File and Directory Entries
API_ https://wicg.github.io/entries-api/, an actively-maintained spec
https://github.com/WICG/entries-api that’s supported in Firefox as well
as in Chrome. So it should not be marked as non-standard.
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data