This builds support for tracking the effect of changes to imports on
other documents, and completes our model for being able to keep
generated code up to date.
- Created a new `Microsoft.VisualStudio.Editor.Razor` assembly to contain Visual Studio platform agnostic info.
- Added a new `Microsoft.VisualStudio.Editor.Razor.Test.Common` project to be the centerfold for all VisualStudio agnostic test pieces.
- Added a `Microsoft.VisualStudio.Editor.Razor.Test` project and pulled in LanguageService test files into the the Editor.Razor.Test project to correspond to their movement in the src project.
#1690