Allow Core Razor editor to work in non-project scenarios.

[NTaylorMullen]

Today if a Razor file is opened outside of the context of a project (diffing two Razor files) there is no IVsHierarchy and therefore no project path or any project information.

Our system relies on the idea that a document conceptually has a project; however, this is not true in the diff scenario and technically not true in the ctrl + o scenario for a Razor file (ctrl + o uses old Razor editor today).

This crashes VS.

[NTaylorMullen]

After investigating what this would entail it led me to believe that our ProjectSnapshot system should not have a file path. This way the idea of a project having a file path can't be a dependency at any layer of the system; it becomes an implementation detail of GetImports and other similar methods on a document or project snapshot.