Fix sample from ApartmentState to GetApartmentState() (#7341)

* Fix sample from `ApartmentState` to `GetApartmentState()`

* Fix `ApartmentTest` sample, a csproj is required now

Author: luizhlelis

samples/snippets/csharp/VS_Snippets_CLR_System/system.Threading.Thread.ApartmentState/CS/ApartmentExample.csproj

@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net48</TargetFramework>
+    <StartupObject>ApartmentTest</StartupObject>
+  </PropertyGroup>
+
+</Project>

samples/snippets/csharp/VS_Snippets_CLR_System/system.Threading.Thread.ApartmentState/CS/source.cs

@@ -11,7 +11,7 @@ static void Main()
         newThread.SetApartmentState(ApartmentState.MTA);
 
         Console.WriteLine("ThreadState: {0}, ApartmentState: {1}", 
-            newThread.ThreadState, newThread.ApartmentState);
+            newThread.ThreadState, newThread.GetApartmentState());
 
         newThread.Start();