Enlarge an xUnit collection to include all ModelMetadataProviders.Current readers

- #41
  - have not seen similar `InvalidOperationException`s in other test classes
- `DisplayExtensionsTest` and `EditorExtensionsTest` are already in this increasingly-poorly named collection
  - they temporarily change `ModelMetadataProviders.Current` to reference a `Mock<ModelMetadataProvider>`

This is a **temporary** fix: should use `[CollectionDefinition(DisableParallelization = true)]` xUnit v2.3.0
  - i.e. create an isolated collection containing just `DisplayExtensionsTest` and `EditorExtensionsTest`

Author: dougbu

test/System.Web.Mvc.Test/Html/Test/DefaultDisplayTemplatesTest.cs

@@ -13,6 +13,7 @@
 
 namespace System.Web.Mvc.Html.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class DefaultDisplayTemplatesTest
     {
         // BooleanTemplate

test/System.Web.Mvc.Test/Test/AssociatedValidatorProviderTest.cs

@@ -9,6 +9,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class AssociatedValidatorProviderTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/CompareAttributeAdapterTest.cs

@@ -9,6 +9,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class CompareAttributeAdapterTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/CompareAttributeTest.cs

@@ -8,6 +8,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class CompareAttributeTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/ControllerActionInvokerTest.cs

@@ -18,6 +18,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class ControllerActionInvokerTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/DataAnnotationsModelValidatorProviderTest.cs

@@ -11,6 +11,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class DataAnnotationsModelValidatorProviderTest
     {
         // Validation attribute adapter registration

test/System.Web.Mvc.Test/Test/DataAnnotationsModelValidatorTest.cs

@@ -10,6 +10,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class DataAnnotationsModelValidatorTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/DefaultModelBinderTest.cs

@@ -15,6 +15,7 @@
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class DefaultModelBinderTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/MaxLengthAttributeAdapterTest.cs

@@ -2,11 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.ComponentModel.DataAnnotations;
-using System.Linq;
 using Microsoft.TestCommon;
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class MaxLengthAttributeAdapterTest
     {
         [Fact]

test/System.Web.Mvc.Test/Test/MinLengthAttributeAdapterTest.cs

@@ -2,11 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.ComponentModel.DataAnnotations;
-using System.Linq;
 using Microsoft.TestCommon;
 
 namespace System.Web.Mvc.Test
 {
+    [Xunit.Collection("Uses ScopeStorage or ViewEngines.Engines")] // Uses ModelMetadataProviders.Current
     public class MinLengthAttributeAdapterTest
     {
         [Fact]