fix(@ngtools/webpack): export VirtualFileSystemDecorator type

We shouldn't need to export this, but webpack-rollup-loader uses it.

Author: filipesilva

packages/ngtools/webpack/src/index.ts

@@ -11,3 +11,6 @@ export * from './interfaces';
 export { ngcLoader as default } from './loader';
 
 export const NgToolsLoader = __filename;
+
+// We shouldn't need to export this, but webpack-rollup-loader uses it.
+export type { VirtualFileSystemDecorator } from './virtual_file_system_decorator';