dotnet-new csproj templates (#4382)

Make csproj templates first-class in dotnet-new.

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

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace WebApplication.Models.AccountViewModels
+{
+    public class RegisterViewModel
+    {
+        [Required]
+        [EmailAddress]
+        [Display(Name = "Email")]
+        public string Email { get; set; }
+
+        [Required]
+        [StringLength(100, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)]
+        [DataType(DataType.Password)]
+        [Display(Name = "Password")]
+        public string Password { get; set; }
+
+        [DataType(DataType.Password)]
+        [Display(Name = "Confirm password")]
+        [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
+        public string ConfirmPassword { get; set; }
+    }
+}