Apply suggestions from code review

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: mcollina

lib/internal/vfs/dir.js

@@ -89,21 +89,16 @@ class VirtualDir {
     }
   }
 
-  [SymbolAsyncIterator]() {
-    return this.entries();
-  }
-
-  [SymbolAsyncDispose]() {
-    return this.close();
-  }
-
   [SymbolDispose]() {
     if (!this.#closed) {
       this.closeSync();
     }
   }
 }
 
+VirtualDir.prototype[SymbolAsyncIterator] = VirtualDir.prototype.entries;
+VirtualDir.prototype[SymbolAsyncDispose] = VirtualDir.prototype.close;
+
 module.exports = {
   VirtualDir,
 };

lib/internal/vfs/file_handle.js

@@ -346,12 +346,11 @@ class VirtualFileHandle {
   closeSync() {
     this[kClosed] = true;
   }
-
-  [SymbolAsyncDispose]() {
-    return this.close();
-  }
 }
 
+VirtualFileHandle.prototype[SymbolAsyncDispose] = VirtualFileHandle.prototype.close;
+VirtualFileHandle.prototype[SymbolDispose] = VirtualFileHandle.prototype.closeSync;
+
 /**
  * A file handle for in-memory file content.
  * Used by MemoryProvider and similar providers.

test/parallel/test-vfs-memory-provider-dynamic.js

@@ -51,8 +51,8 @@ function makeFileEntry(prototypeFrom, contentProvider) {
   const provider = new MemoryProvider();
   const root = getRoot(provider);
 
-  const dir = { __proto__: Object.getPrototypeOf(root) };
-  Object.assign(dir, {
+  const dir = {
+    __proto__: Object.getPrototypeOf(root),
     type: 1,           // TYPE_DIR
     mode: 0o755,
     children: new Map(),