Add nesting of csproj under slnx files

Author: jbevain

Packages/com.unity.ide.visualstudio/Editor/VisualStudioCodeInstallation.cs

@@ -382,6 +382,7 @@ private void CreateSettingsFile(string vscodeDirectory, bool enablePatch)
     ""explorer.fileNesting.enabled"": true,
     ""explorer.fileNesting.patterns"": {
         ""*.sln"": ""*.csproj"",
+        ""*.slnx"": ""*.csproj""
     },
     ""dotnet.defaultSolution"": """ + IOPath.GetFileName(ProjectGenerator.SolutionFile()) + @"""
 }";