Stub Annotation classes for consistent use of Prefix

Author: mhutch

src/System.CommandLine.Subsystems/CompletionSubsystem.cs

@@ -2,13 +2,14 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.CommandLine.Subsystems;
+using System.CommandLine.Subsystems.Annotations;
 
 namespace System.CommandLine;
 
 public class CompletionSubsystem : CliSubsystem
 {
     public CompletionSubsystem(IAnnotationProvider? annotationProvider = null)
-        : base("Completion", annotationProvider, SubsystemKind.Completion)
+        : base(CompletionAnnotations.Prefix, annotationProvider, SubsystemKind.Completion)
     { }
 
     // TODO: Figure out trigger for completions

src/System.CommandLine.Subsystems/ErrorReportingSubsystem.cs

@@ -2,13 +2,14 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.CommandLine.Subsystems;
+using System.CommandLine.Subsystems.Annotations;
 
 namespace System.CommandLine;
 
 public class ErrorReportingSubsystem : CliSubsystem
 {
     public ErrorReportingSubsystem(IAnnotationProvider? annotationProvider = null)
-        : base("ErrorReporting", annotationProvider, SubsystemKind.ErrorReporting)
+        : base(ErrorReportingAnnotations.Prefix, annotationProvider, SubsystemKind.ErrorReporting)
     { }
 
     // TODO: Stash option rather than using string

src/System.CommandLine.Subsystems/Subsystems/Annotations/CompletionAnnotations.cs

@@ -0,0 +1,12 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace System.CommandLine.Subsystems.Annotations;
+
+/// <summary>
+/// IDs for well-known Completion annotations.
+/// </summary>
+public static class CompletionAnnotations
+{
+    public static string Prefix { get; } = nameof(SubsystemKind.Completion);
+}

src/System.CommandLine.Subsystems/Subsystems/Annotations/ErrorReportingAnnotations.cs

@@ -0,0 +1,12 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace System.CommandLine.Subsystems.Annotations;
+
+/// <summary>
+/// IDs for well-known ErrorReporting annotations.
+/// </summary>
+public static class ErrorReportingAnnotations
+{
+    public static string Prefix { get; } = nameof(SubsystemKind.ErrorReporting);
+}

src/System.CommandLine.Subsystems/VersionSubsystem.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.CommandLine.Subsystems;
+using System.CommandLine.Subsystems.Annotations;
 using System.Reflection;
 
 namespace System.CommandLine;
@@ -11,11 +12,10 @@ public class VersionSubsystem : CliSubsystem
     private string? specificVersion = null;
 
     public VersionSubsystem(IAnnotationProvider? annotationProvider = null)
-        : base("Version", annotationProvider, SubsystemKind.Version)
+        : base(VersionAnnotations.Prefix, annotationProvider, SubsystemKind.Version)
     {
     }
 
-
     // TODO: Should we block adding version anywhere but root?
     public string? SpecificVersion
     {