Registration of toolbar factory functions...

... reduces direct dependencies of ToolManager.cpp.

This frees four files from cycles:
DeviceToolBar
EditToolBar
MeterToolBar
MixerToolBar

Leaving 66 files still in the big s.c.c.

src/toolbars/TranscriptionToolBar.cpp

@@ -980,3 +980,7 @@ void TranscriptionToolBar::AdjustPlaySpeed(float adj)
    OnSpeedSlider(e);
 }
 
+static RegisteredToolbarFactory factory{ TranscriptionBarID,
+   [](AudacityProject *){
+      return ToolBar::Holder{ safenew TranscriptionToolBar }; }
+};