Don't hard-code the exhaustive list of sub-view types...

... in Wave track context menu and SetTrackVisualsCommand

Instead, discover them through a registry.

This eliminates some duplication of string constants and prepares for
non-intrusive generalization to more kinds of sub-views.

This makes the command agnostic about which subview types are known, but the
context menu still has special case treatment for Spectrogram Settings and
Wave Colors.

src/tracks/playabletrack/wavetrack/ui/WaveTrackView.cpp

@@ -40,6 +40,53 @@ Paul Licameli split from TrackPanel.cpp
 #include "../../../ui/ButtonHandle.h"
 #include "../../../../TrackInfo.h"
 
+namespace {
+   class Registry {
+   public:
+      using Type = WaveTrackSubView::Type;
+      using Types = std::vector< Type >;
+
+      void Append( Type type )
+      {
+         types.emplace_back( std::move( type ) );
+         sorted = false;
+      }
+
+      Types &Get()
+      {
+         if ( !sorted ) {
+            auto begin = types.begin(), end = types.end();
+            std::sort( begin, end );
+            // We don't want duplicate ids!
+            wxASSERT( end == std::adjacent_find( begin, end ) );
+            sorted = true;
+         }
+         return types;
+      }
+
+   private:
+      Types types;
+      bool sorted = false;
+   };
+
+   Registry &GetRegistry()
+   {
+      static Registry result;
+      return result;
+   }
+}
+
+WaveTrackSubView::RegisteredType::RegisteredType( Type type )
+{
+   GetRegistry().Append( std::move( type ) );
+}
+
+// static
+auto WaveTrackSubView::AllTypes() -> const Types &
+{
+   return GetRegistry().Get();
+}
+
 namespace {
 
 using WaveTrackSubViewPtrs = std::vector< std::shared_ptr< WaveTrackSubView > >;