feat(loader): add private field to loader's package.json (#3566)

this commit adds `private: true` to the `package.json`file
that is generated for the `loader/` directory upon building
a stencil project.

src/compiler/output-targets/output-lazy-loader.ts

@@ -32,6 +32,7 @@ const generateLoader = async (
   const packageJsonContent = JSON.stringify(
     {
       name: config.fsNamespace + '-loader',
+      private: true,
       typings: './index.d.ts',
       module: './index.js',
       main: './index.cjs.js',