dotnet-new csproj templates (#4382)

Make csproj templates first-class in dotnet-new.

TestAssets/TestProjects/ProjectJsonWebTemplate/Models/ManageViewModels/FactorViewModel.cs

@@ -0,0 +1,12 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace WebApplication.Models.ManageViewModels
+{
+    public class FactorViewModel
+    {
+        public string Purpose { get; set; }
+    }
+}