Accessors to get the project window...

... as a preparation for splitting up class AudacityProject.

Use ProjectWindow as an alias for AudacityProject, and fetch it from the
project with a static member function, where certain of its services are used;
pretending they are not the same class.

Use global accessor functions to get wxFrame from the project where only
wxFrame's member functions are needed, so there will be less dependency on
ProjectWindow when it becomes a distinct class.

src/LabelTrack.cpp

@@ -2180,7 +2180,7 @@ void LabelTrack::ShowContextMenu()
 
    // Bug 2044.  parent can be nullptr after a context switch.
    if( !parent )
-      parent = GetActiveProject();
+      parent = FindProjectFrame( GetActiveProject() );
 
    if( parent )
    {
@@ -3091,8 +3091,9 @@ void LabelTrack::DoEditLabels
    auto &trackFactory = TrackFactory::Get( project );
    auto rate = project.GetRate();
    auto &viewInfo = ViewInfo::Get( project );
+   auto &window = ProjectWindow::Get( project );
 
-   LabelDialog dlg(&project, trackFactory, &tracks,
+   LabelDialog dlg(&window, trackFactory, &tracks,
                    lt, index,
                    viewInfo, rate,
                    format, freqFormat);
@@ -3102,7 +3103,7 @@ void LabelTrack::DoEditLabels
 
    if (dlg.ShowModal() == wxID_OK) {
       project.PushState(_("Edited labels"), _("Label"));
-      project.RedrawProject();
+      window.RedrawProject();
    }
 }
 
@@ -3121,7 +3122,8 @@ int LabelTrack::DialogForLabelName(
       -40;
    position.y += 2;  // just below the bottom of the track
    position = trackPanel.ClientToScreen(position);
-   AudacityTextEntryDialog dialog{ &project,
+   auto &window = GetProjectFrame( project );
+   AudacityTextEntryDialog dialog{ &window,
       _("Name:"),
       _("New label"),
       initialValue,
@@ -3130,7 +3132,7 @@ int LabelTrack::DialogForLabelName(
 
    // keep the dialog within Audacity's window, so that the dialog is always fully visible
    wxRect dialogScreenRect = dialog.GetScreenRect();
-   wxRect projScreenRect = project.GetScreenRect();
+   wxRect projScreenRect = window.GetScreenRect();
    wxPoint max = projScreenRect.GetBottomRight() + wxPoint{ -dialogScreenRect.width, -dialogScreenRect.height };
    if (dialogScreenRect.x > max.x) {
       position.x = max.x;