Change, clean, refactor class SelectExpandNode in vNext

[xuzhg]

Short summary (3-5 sentences) describing the issue.

Assemblies affected

*Which assemblies and versions are known to be affected e.g. OData WebApi lib 8.x

Introduction

In the increment, SelectExpandNode has been changed a lot.

Currently, its structure looks not a good design, for example, for properties' naming.

In the next version of webapi, please consider to redesign this class.