Use full 4x4 matrix for mapRect operation in Transform layer #130303
Description
After fixing #82961, we drop down to a 3x3 matrix here: https://github.com/flutter/engine/blob/b9b1b63c2ba99c149f2846ac1c5430084f2ec346/flow/layers/transform_layer.cc#L49
We should do the rect mapping using the full 4x4 transform. Skia has an implementation for this in SkMatrixPriv.
@flar fyi