[two_dimensional_scrollables] Fix span border decorations in flipped cross axes

[Piinks]

Fixes flutter/flutter#177117

Fixes an issue in two_dimensional_scrollables where TableSpan vertical borders were incorrectly flipped when ScrollableDetails.horizontal was reversed.

The SpanBorder.paint method previously used its own axisDirection to determine leading and trailing edge flipping for a cross-axis border component. This works in natural scrolling directions, but creates an inverted orientation assumption when the perpendicular axis is reversed.

Does not affect TreeView, since that widget does not allow for reversed axes.

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Code Review

This pull request fixes an issue where TableSpan borders were flipped when one or both axis directions were reversed. The fix involves introducing a crossAxisDirection parameter to SpanDecorationPaintDetails and updating the SpanBorder.paint method to use this new parameter for accurate border rendering. The RenderTableViewport and RenderTreeViewport classes were updated to pass the appropriate cross-axis direction. A new test case was added to verify the fix for a reversed horizontal axis. The reviewer suggests adding an additional test case for a row span with a reversed vertical axis to improve test coverage.

[AbdeMohlbi]

SGTM, do we need to link to the issue from that test ie: test for issue177777 for example ?

[Piinks]

SGTM, do we need to link to the issue from that test ie: test for issue177777 for example ?

Oh good call! I will add the regression test references, thanks!