Unify wxGrid code for processing row and column mouse events

Reuse the same code for handling mouse events for both rows and columns
instead of duplicating almost (but not quite) the same code for both of
them.

As part of resolving the inconsistencies between the two versions, add
wxEVT_GRID_ROW_AUTO_SIZE corresponding to the existing event with the
same name for the columns.

Closes #22380.

samples/grid/griddemo.cpp

@@ -1564,6 +1564,7 @@ void GridFrame::FreezeOrThaw(wxCommandEvent& ev)
     }
 
     GetMenuBar()->Enable( ID_TOGGLECOLMOVING, !grid->IsFrozen() );
+    GetMenuBar()->Enable( ID_TOGGLEROWMOVING, !grid->IsFrozen() );
 }
 
 void GridFrame::SetCellFgColour( wxCommandEvent& WXUNUSED(ev) )