Respect code style option severity in ConvertSwitchStatementToExpressionDiagnosticAnalyzer

Fixes #36086

src/EditorFeatures/CSharpTest/ConvertSwitchStatementToExpression/ConvertSwitchStatementToExpressionTests.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CodeStyle;
+using Microsoft.CodeAnalysis.CSharp.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.ConvertSwitchStatementToExpression;
 using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Diagnostics;
+using Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces;
 using Microsoft.CodeAnalysis.Test.Utilities;
+using Roslyn.Test.Utilities;
 using Xunit;
 
 namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.ConvertSwitchStatementToExpression
@@ -624,5 +629,36 @@ int M(int i)
     }
 }");
         }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsConvertSwitchStatementToExpression)]
+        [WorkItemAttribute(36086, "https://github.com/dotnet/roslyn/issues/36086")]
+        public async Task TestSeverity()
+        {
+            var source =
+@"class Program
+{
+    int M(int i)
+    {
+        [||]switch (i)
+        {
+            case 1:
+                return 4;
+            case 2:
+                return 5;
+            case 3:
+                return 6;
+            default:
+                return 7;
+        }
+    }
+}";
+            var warningOption = new CodeStyleOption<bool>(true, NotificationOption.Warning);
+            var options = Option(CSharpCodeStyleOptions.PreferSwitchExpression, warningOption);
+            var testParameters = new TestParameters(options: options, parseOptions: TestOptions.Regular8);
+            using var workspace = CreateWorkspaceFromOptions(source, testParameters);
+            var diags = await GetDiagnosticsAsync(workspace, testParameters);
+            Assert.Single(diags);
+            Assert.Equal(DiagnosticSeverity.Warning, diags.First().Severity);
+        }
     }
 }

src/Features/CSharp/Portable/ConvertSwitchStatementToExpression/ConvertSwitchStatementToExpressionDiagnosticAnalyzer.cs

@@ -61,9 +61,10 @@ private void AnalyzeSyntax(SyntaxNodeAnalysisContext context)
                 return;
             }
 
-            context.ReportDiagnostic(Diagnostic.Create(Descriptor,
+            context.ReportDiagnostic(DiagnosticHelper.Create(Descriptor,
                 // Report the diagnostic on the "switch" keyword.
                 location: switchStatement.GetFirstToken().GetLocation(),
+                effectiveSeverity: styleOption.Notification.Severity,
                 additionalLocations: new[] { switchStatement.GetLocation() },
                 properties: ImmutableDictionary<string, string>.Empty
                     .Add(Constants.NodeToGenerateKey, ((int)nodeToGenerate).ToString(CultureInfo.InvariantCulture))