3DBox: box3d-tool: set box3d->transform when first creating the 3dbox (drag) and call doWriteTransform when finished

3DBox: box3d-tool: set box3d->transform when first creating the 3dbox (drag) and call doWriteTransform when finished.

Fixes #5950 (closed), and #4395 (closed), #5704 (closed), #4232 (closed)

Also fix scaling of stroke width when resizing objects (both with and without /options/transform/stroke)

• Call updateRepr() before adjusting stroke to work around SPStyle::read clearing the new stroke
• ObjectSet::applyAffine: Explicitly pass transform to doWriteTransform so sp_item_transform_repr doesn't just cancel out the transform and break adjust_stroke compensation.