Make sure culture info is persisted across methods executed from classes with UseCulture attribute

When we change the current thread's culture, that change is lost
when an async method is called. So Microsoft guys have introduced
the CultureInfo.DefaultThreadCurrentCulture property in .NET 4.5.

See https://stackoverflow.com/a/30664385/1396155

According to this SO answer, we do not have to use this property
in .NET 4.6 because async methods seem to get the same culture info
the caller method has. So if someday the test project's target
framework is updated, feel free to revert this commit.

Author: monoblaine

StyleCop.Analyzers/StyleCop.Analyzers.Test/Helpers/UseCultureAttribute.cs

@@ -33,6 +33,10 @@ public class UseCultureAttribute : BeforeAfterTestAttribute
 
         private CultureInfo originalUiCulture;
 
+        private CultureInfo originalDefaultCulture;
+
+        private CultureInfo originalDefaultUiCulture;
+
         /// <summary>
         /// Initializes a new instance of the <see cref="UseCultureAttribute"/>
         /// class with a culture.
@@ -85,9 +89,14 @@ public override void Before(MethodInfo methodUnderTest)
         {
             this.originalCulture = Thread.CurrentThread.CurrentCulture;
             this.originalUiCulture = Thread.CurrentThread.CurrentUICulture;
+            this.originalDefaultCulture = CultureInfo.DefaultThreadCurrentCulture;
+            this.originalDefaultUiCulture = CultureInfo.DefaultThreadCurrentUICulture;
 
             Thread.CurrentThread.CurrentCulture = this.Culture;
             Thread.CurrentThread.CurrentUICulture = this.UiCulture;
+
+            CultureInfo.DefaultThreadCurrentCulture = this.Culture;
+            CultureInfo.DefaultThreadCurrentUICulture = this.UiCulture;
         }
 
         /// <summary>
@@ -99,6 +108,9 @@ public override void After(MethodInfo methodUnderTest)
         {
             Thread.CurrentThread.CurrentCulture = this.originalCulture;
             Thread.CurrentThread.CurrentUICulture = this.originalUiCulture;
+
+            CultureInfo.DefaultThreadCurrentCulture = this.originalDefaultCulture;
+            CultureInfo.DefaultThreadCurrentUICulture = this.originalDefaultUiCulture;
         }
     }
 }