Keep the drawing transform when drawing meshing in CanvasItem

[groud]

Fixes #49825

Tested on my side, seems to work fine.

[lawnjelly]

As far as I remember, the logic around these extra transforms (and having them present separately from the main transform in the shaders) ended up being quite problematic in terms of implementation in 3.x. They may have been introduced originally for instancing. It might be worth considering in 4.x whether it could be worth simplifying this whole area.

For instance just have the extra transforms multiply with the existing transform for the item, and therefore apply to all further commands, update the main transform to the shader, but not keep the separation between main and extra transform. (This separation may have already been dropped in 4.x, I haven't examined the shaders.)

[akien-mga]

Thanks!