dotnet-new csproj templates (#4382)

Make csproj templates first-class in dotnet-new.

TestAssets/TestProjects/ProjectJsonWebTemplate/Models/AccountViewModels/LoginViewModel.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace WebApplication.Models.AccountViewModels
+{
+    public class LoginViewModel
+    {
+        [Required]
+        [EmailAddress]
+        public string Email { get; set; }
+
+        [Required]
+        [DataType(DataType.Password)]
+        public string Password { get; set; }
+
+        [Display(Name = "Remember me?")]
+        public bool RememberMe { get; set; }
+    }
+}