[roll] Roll fuchsia [fdio] Refactor to use fbl::RefPtr

- Create internal APIs that transact in RefPtr
- Move exported APIs to files matching header names
- Avoid exported APIs whenever possible internally

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/500060
Original-Revision: 83f4c24fe96daa2c5535329415bd32c0ca9d90dd
GitOrigin-RevId: 44f8567e604d4e56799292b14f1618fe97ef6ae5
Change-Id: I556f4560d8385609b9b0f36f8056d804ac1fa237
diff --git a/stem b/stem
index 2f265d7..e495831 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="caa18786154f6603510f9b333659bb1262e85e79"/>
+             revision="83f4c24fe96daa2c5535329415bd32c0ca9d90dd"/>
   </projects>
   <hooks>
     <hook name="install-environment"