vtkPlotBar: Account for shift scale in bar width calculation

The bar width calculation in vtkChartXY::CalculateBarPlots did not consider the shift and scale transformations applied to the bar's input data. This resulted in incorrectly sized bars when a shift or scale was active.

This commit corrects the calculation by applying the shift and scale to the x-coordinates before computing the width, ensuring the bar widths are rendered correctly.

Fixes #19791 (closed)

Backport: release