FSA: Relax file name checks in the BucketFS

Unlike when saving files to the local file system, the names of files in
the the Bucket File System (a.k.a. OPFS) are obfuscated before they end
up on disk - if they even end up on disk at all.

As such, we don't need to perform the same name sanitization and
obfuscation for these files as we do for files that end up on the
user-visible file system.

See whatwg/fs#93 for context

Bug: 1399536
Change-Id: I019b393b731cd20aa4c45eade4eca19b6633e9cd

fs/resources/test-helpers.js

@@ -5,13 +5,9 @@ const kCurrentDirectory = '.';
 const kParentDirectory = '..';
 
 // Array of separators used to separate components in hierarchical paths.
-let kPathSeparators;
-if (navigator.userAgent.includes('Windows NT')) {
-  // Windows uses both '/' and '\' as path separators.
-  kPathSeparators = ['/', '\\'];
-} else {
-  kPathSeparators = ['/'];
-}
+// Consider both '/' and '\' as path separators to ensure file names are
+// platform-agnostic.
+let kPathSeparators = ['/', '\\'];
 
 async function getFileSize(handle) {
   const file = await handle.getFile();