Add an API for ProjectState.AnalyzerConfigDocumentIds to be consistent

It's not as important as the others because the file ordering doesn't
matter in the same way, but it's good to have for consistency.

src/Workspaces/Core/Portable/Workspace/Solution/Project.cs

@@ -173,7 +173,7 @@ internal Project(Solution solution, ProjectState projectState)
         /// <summary>
         /// All the <see cref="AnalyzerConfigDocument"/>s associated with this project.
         /// </summary>
-        public IEnumerable<AnalyzerConfigDocument> AnalyzerConfigDocuments => _projectState.AnalyzerConfigDocumentStates.Select(s => GetAnalyzerConfigDocument(s.Key));
+        public IEnumerable<AnalyzerConfigDocument> AnalyzerConfigDocuments => _projectState.AnalyzerConfigDocumentIds.Select(GetAnalyzerConfigDocument);
 
         /// <summary>
         /// True if the project contains a document with the specified ID.

src/Workspaces/Core/Portable/Workspace/Solution/ProjectState.cs

@@ -402,6 +402,11 @@ public async Task<VersionStamp> GetSemanticVersionAsync(CancellationToken cancel
         [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
         public IReadOnlyList<DocumentId> AdditionalDocumentIds => _additionalDocumentIds;
 
+        [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
+        // Regular documents and additionald documents have an ordering, and so we maintain lists of the IDs in order; in the case of analyzerconfig documents,
+        // we don't define a workspace ordering because they are ordered via fancier algorithms in the compiler based on directory depth.
+        public IEnumerable<DocumentId> AnalyzerConfigDocumentIds => _analyzerConfigDocumentStates.Keys;
+
         [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
         public IImmutableDictionary<DocumentId, DocumentState> DocumentStates => _documentStates;