Add wxBitmapBundle::GetPreferredLogicalSizeFor()

We often need the logical bitmap size when using it in size computations
involving window size, so add a function returning it directly to
wxBitmapBundle, similarly to wxBitmap::GetLogicalSize(), to avoid using
FromPhys() everywhere.

Also rename the existing wxBitmapBundle::GetPreferredSizeFor() to
GetPreferredBitmapSizeFor() to make it more clear that this is similar
to wxBitmap::GetSize() and so returns the size in physical units.

Closes #22056.

samples/treectrl/treetest.cpp

@@ -1015,7 +1015,7 @@ void MyTreeCtrl::CreateImages(int size)
             return m_sizeDef;
         }
 
-        wxSize GetPreferredSizeAtScale(double scale) const wxOVERRIDE
+        wxSize GetPreferredBitmapSizeAtScale(double scale) const wxOVERRIDE
         {
             return m_sizeDef*scale;
         }