fix: use isFileInFolder for cross-platform opaque whiteout dir matching

isFileInOpaqueDir was using path.dirname and path.sep directly, which
breaks on Windows where path.sep is \ but Docker paths use /. Reuse
the existing isFileInFolder helper which normalizes paths first —
same pattern as isFileInARemovedFolder.

Author: parker-snyk

lib/extractor/index.ts

@@ -310,13 +310,9 @@ function isFileInOpaqueDir(
   filename: string,
   opaqueWhiteoutDirs: Set<string>,
 ): boolean {
-  const dir = path.dirname(filename);
-  for (const opaqueDir of opaqueWhiteoutDirs) {
-    if (dir === opaqueDir || dir.startsWith(opaqueDir + path.sep)) {
-      return true;
-    }
-  }
-  return false;
+  return Array.from(opaqueWhiteoutDirs).some((opaqueDir) =>
+    isFileInFolder(filename, opaqueDir),
+  );
 }
 
 /**