[3.x] Physics Interpolation - Fix 2D skinning

[lawnjelly]

2D skinning required the interpolated skeleton base transform to be updated when using interpolation.

Fixes #92872

Notes

• The MRP needs to set interpolation to on for the skeleton for this to work (this turns on the machinery).
• The skeleton processing throttles off automatically when hidden.

[Calinou]

Tested locally, it works as expected. Behavior is still correct when physics interpolation is disabled.

Code looks good to me.

Before

skeleton_3.x_master.mp4

After

skeleton_3.x_pr.mp4

[lawnjelly]

Thanks!