Pass filekind through the workspace layer

This commit enables us to initialize projects with the correct file
kind, thus allowing mixed views and components in the same project.

This isn't hooked up to MSBuild yet, so for now nothing will initialize
this code with the correct file kind.
\n\nCommit migrated from 7216d18cfb

src/Razor/perf/Microsoft.AspNetCore.Razor.Performance/ProjectSystem/ProjectSnapshotManagerBenchmarkBase.cs

@@ -45,7 +45,7 @@ namespace Microsoft.AspNetCore.Razor.Performance
             for (var i = 0; i < Documents.Length; i++)
             {
                 var filePath = Path.Combine(projectRoot, "Views", "Home", $"View00{i % 4}.cshtml");
-                Documents[i] = new HostDocument(filePath, $"/Views/Home/View00{i}.cshtml");
+                Documents[i] = new HostDocument(filePath, $"/Views/Home/View00{i}.cshtml", FileKinds.Legacy);
             }
 
             var tagHelpers = Path.Combine(root.FullName, "benchmarks", "Microsoft.AspNetCore.Razor.Performance", "taghelpers.json");