Merge pull request #14015 from michaelnebel/csharp/vscodesettings

C#: Update of VS Code settings.

Author: michaelnebel

csharp/.vscode/extensions.json

@@ -1,9 +1,11 @@
 {
     "recommendations": [
+        "formulahendry.dotnet-test-explorer",
+        "gaoshan0621.csharp-format-usings",
         "github.vscode-codeql",
+        "hbenl.vscode-test-explorer",
         "ms-dotnettools.csharp",
-        "formulahendry.dotnet-test-explorer",
-        "hbenl.vscode-test-explorer"
+        "ms-dotnettools.csdevkit"
     ],
     "unwantedRecommendations": []
 }

csharp/.vscode/settings.json

@@ -7,5 +7,8 @@
         "editor.defaultFormatter": "ms-dotnettools.csharp"
     },
     "omnisharp.enableEditorConfigSupport": true,
-    "omnisharp.enableRoslynAnalyzers": true
+    "omnisharp.enableRoslynAnalyzers": true,
+    "csharpFormatUsings.splitGroups": false,
+    "csharpFormatUsings.sortOrder": "Xunit System Microsoft Semmle.Util Semmle",
+    "dotnet.defaultSolution": "CSharp.sln"
 }