Compilation of Views should be affected by changes to _ViewStart files

that are applicable to the view.

Fixes #974
From a DI perspective creating this type was being problematic since `MvcRazorHost` would require an instance of it to compile which leads to a cyclic dependency. Given that the behavior of this type can be replaced by replacing the `IRazorPageFactory`, I changed it be replaced by a utility type that both `VirtualPathRazorPageFactory` and `MvcRazorHost` depend on.