[roll] Roll fuchsia [f2fs_reader] aes256xts support for tests.

The crypto here isn't intended to be used in production but, I
wanted to make sure that there was a test for file content reading.

fxfs-crypto's XTS implementation differs sufficiently enough that I
didn't want to share it.

Also took the liberty of hiding more internal state.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1237884
Original-Revision: cb3f5268683a96de7b8e40c3914e40ff09fbfd74
GitOrigin-RevId: 54d3ff1ba01acc3150ca71024c4aacd33b7a5903
Change-Id: I4bc8ccfc76815f0aefd71c906e877bf9e3e3a6d4
diff --git a/stem b/stem
index cb40a41..adfd1f8 100644
--- a/stem
+++ b/stem
@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="1d516a6ef5f4560a39292e340b8032b71588cd35"/>
+             revision="cb3f5268683a96de7b8e40c3914e40ff09fbfd74"/>
   </projects>
   <hooks>
     <hook name="install-environment"