Add more FSStatFlags and add FSTimeToCalendarTime

[Crementif]

This pull request adds:

• Missing flags to FSStatFlags so that it's possible to recognize these (sym)links or encrypted files.
• Adds the FSTimeToCalendarTime function which is used to convert the created and modified time of the FSStat entry.

These additions don't change anything and are only additive, so it won't break/change existing projects. I also added doxygen comments to make it clearer what each one entails. There are more flags, but none that I can make sense of.

Credits to @koolkdev for figuring out the FSStat flags. I double-checked them and did some minor changes (unencrypted -> encrypted).

[exjam]

Merged as https://github.com/devkitPro/wut/commit/7831bb20a1202dc51a14bcef47521dcfdfe0a5d4

(renamed parameter to *outCalendarTime)

[exjam]

Thanks !