[FSA] Update documentation links

These changes were originally proposed in this refactor [1], but have
been split into another CL.

Bug: 1110509
Change-Id: Ifa430ebd8b39eaed9773a2b9ca6e4963f2d40002
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2604974
Commit-Queue: Austin Sullivan <asully@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Auto-Submit: Austin Sullivan <asully@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841550}

third_party/blink/renderer/modules/file_system_access/data_transfer_item_file_system_access.idl

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// https://wicg.github.io/file-system-access/#drag-and-drop
 [
     ImplementedAs=DataTransferItemFileSystemAccess,
     RuntimeEnabled=FileSystemAccess

third_party/blink/renderer/modules/file_system_access/file_system_directory_iterator.idl

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 // Async iterator returned by FileSystemDirectoryHandle.getEntries().
-// https://github.com/WICG/writable-files/blob/master/EXPLAINER.md
+// https://wicg.github.io/file-system-access/#api-filesystemdirectoryhandle-asynciterable
 // https://www.ecma-international.org/ecma-262/9.0/index.html#sec-asynciterator-interface
 [
     LegacyNoInterfaceObject,

third_party/blink/renderer/modules/file_system_access/window_file_system_access.idl

@@ -2,8 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// https://wicg.github.io/native-file-system/#native-filesystem
-// https://wicg.github.io/native-file-system/#api-getoriginprivatefilesystem
+// https://wicg.github.io/file-system-access/#local-filesystem
 [
     SecureContext,
     RuntimeEnabled=FileSystemAccess,