The project snapshot now maintains a RazorProjectEngine as well as set
of Tag Helpers that are known for that snapshot.
Pivoted some more services to be snapshot-centric.
Also added the ability to track .cshtml documents to the project system.
For now most components just ignore document changes.
- Instead of using Razor/Mvc TemplateEngine use `RazorProjectEngine`. This involved changing several locations (each of which used `RazorTemplateEngine` in an entirely different way) to use the RazorProjectEngine's two Process methods.
- Changed an unused public API `VisualStudioRazorParser.TemplateEngine` to `VisualStudioRazorParser.RazorProjectEngine`.
- Ported the remainder of `RazorEngineBuilder`'s extension methods over to `RazorProjectEngineBuilder`. These were used in tests and our `RazorGenerate` tool.
- Added a few test helper methods/classes to enable simple testing of the `RazorProjectEngine`.
- Resolved several test hacks that were working around little discrepancies each of the `RazorTemplateEngine` APIs.
- Changed the template engine factory service to be a project engine factory service.
- Added a `FileChangeTracker`, `FileChangeTrackerFactory` and corresponding implementations. These types now enable us to implement Windows and Mac file change tracking instead of replacing the entire import manager.
- Changed the import manager to be a Roslyn based service.
- Moved import manager implementation to the editor.razor assembly now since it no longer depends on windows.
- Updated import manager unit tests.
- Added import manager integration test
- Added file change tracking tests.
#1804