Cell range selection only works correctly when columns stay in original order

[PatrickN-GH]

I am using the relatively new feature cell selection and observed the following issue:
When selecting multiple cells with the Shift key pressed, the resulting selection is not as expected when columns have been reordered. This is because the direction of selection from the start cell is determined by comparing column indices instead of the actual column position, which would be the correct way. This happens in unit VirtualTrees.BaseTree.pas and affects (at least) procedures "ToggleCellSelection", "InternalSelectCells" and "InternalUnselectCells".