Change hardcoded usage of Microsoft.CSharp.CSharpProvider to instantiate it using CodeDomProvider.CreateProvider

Change hardcoded usage of Microsoft.CSharp.CSharpProvider to instantiate it using CodeDomProvider.CreateProvider

This gives the flexibility to configure dynamic compilation via app/web.config, ie. using Roslyn for newer C# features.

Implements feature #735

该提问来源于开源项目：Orckestra/C1-CMS-Foundation