The Transform node sets its GraphicGroup's final transform, but should only affect the data-so-far in the graph flow

[Keavon]

If you stick a Transform node underneath a layer stack, the whole stack gets moved even though, intuitively, it's applying to no data in the stack so far. If you stick the Transform node/layer in the middle of a stack, it affects both those layers above and below it. Definitely feels wrong.

That's because it is changing the final resulting GraphicGroup's transform field, instead of the transform on the individual layers up to that point which make up the partial stack (the part underneath the transform node).

The tricky part is preserving the correct behavior for rendering strokes (or gradient fills) which can get stretched and skewed.

This relates to #1930 and #1834.