Fix race condition in CodeFixService

Ensure that we process diagnostics ordered by their span and then diagnostic ID. This fixes a race condition seen in intermittent failures for ConfigureCodeStyleOptionValueAndSeverity where the order of configuration/suppression fixes is non-deterministic

src/EditorFeatures/Core/Implementation/CodeFixes/CodeFixService.cs

@@ -160,7 +160,8 @@ public async Task<ImmutableArray<CodeFixCollection>> GetFixesAsync(Document docu
 
             // group diagnostics by their diagnostics span
             // invariant: later code gathers & runs CodeFixProviders for diagnostics with one identical diagnostics span (that gets set later as CodeFixCollection's TextSpan)
-            Dictionary<TextSpan, List<DiagnosticData>>? aggregatedDiagnostics = null;
+            // order diagnostics by span and then diagnostic ID.
+            SortedDictionary<TextSpan, SortedList<DiagnosticId, DiagnosticData>>? aggregatedDiagnostics = null;
             foreach (var diagnostic in await _diagnosticService.GetDiagnosticsForSpanAsync(document, range, diagnosticIdOpt: null, includeConfigurationFixes, addOperationScope, cancellationToken).ConfigureAwait(false))
             {
                 if (diagnostic.IsSuppressed)
@@ -170,8 +171,8 @@ public async Task<ImmutableArray<CodeFixCollection>> GetFixesAsync(Document docu
 
                 cancellationToken.ThrowIfCancellationRequested();
 
-                aggregatedDiagnostics ??= new Dictionary<TextSpan, List<DiagnosticData>>();
-                aggregatedDiagnostics.GetOrAdd(diagnostic.GetTextSpan(), _ => new List<DiagnosticData>()).Add(diagnostic);
+                aggregatedDiagnostics ??= new SortedDictionary<TextSpan, SortedList<string, DiagnosticData>>();
+                aggregatedDiagnostics.GetOrAdd(diagnostic.GetTextSpan(), _ => new SortedList<DiagnosticId, DiagnosticData>()).Add(diagnostic.Id, diagnostic);
             }
 
             if (aggregatedDiagnostics == null)
@@ -184,7 +185,7 @@ public async Task<ImmutableArray<CodeFixCollection>> GetFixesAsync(Document docu
             foreach (var spanAndDiagnostic in aggregatedDiagnostics)
             {
                 await AppendFixesAsync(
-                    document, spanAndDiagnostic.Key, spanAndDiagnostic.Value, fixAllForInSpan: false, isBlocking,
+                    document, spanAndDiagnostic.Key, spanAndDiagnostic.Value.Values, fixAllForInSpan: false, isBlocking,
                     result, addOperationScope, cancellationToken).ConfigureAwait(false);
             }
 
@@ -204,7 +205,7 @@ int GetValue(CodeFixCollection c)
                 foreach (var spanAndDiagnostic in aggregatedDiagnostics)
                 {
                     await AppendConfigurationsAsync(
-                        document, spanAndDiagnostic.Key, spanAndDiagnostic.Value,
+                        document, spanAndDiagnostic.Key, spanAndDiagnostic.Value.Values,
                         result, cancellationToken).ConfigureAwait(false);
                 }
             }