Add File System (worth prototyping) (mozilla#614)

Note that the linked issue is technically for AccessHandle which will be part of this standard (but are not yet). It seems good to have a position on the full standard that will eventually include it.

activities.json

@@ -483,6 +483,19 @@
     "title": "File Handling",
     "url": "https://github.com/WICG/file-handling/blob/master/explainer.md"
   },
+  {
+    "ciuName": null,
+    "description": "File System defines infrastructure for file systems as well as their API.",
+    "id": "fs",
+    "mdnUrl": null,
+    "mozBugUrl": "https://bugzilla.mozilla.org/show_bug.cgi?id=1748667",
+    "mozPosition": "worth prototyping",
+    "mozPositionDetail": "A storage endpoint with a POSIX-like file system API is a valuable addition to the web platform.",
+    "mozPositionIssue": 562,
+    "org": "WHATWG",
+    "title": "File System",
+    "url": "https://fs.spec.whatwg.org/"
+  },
   {
     "ciuName": "native-filesystem-api",
     "description": "This document defines a web platform API that lets websites gain write access to the local file system. It builds on File API, but adds lots of new functionality on top.",