STL skipAnimation should depends on canChangeContent

We now check the conditions to skip the animation after computing the
current targetContent.
This helps avoid unexpected jump cut animations.

Test: atest DraggableHandlerTest
Test: manually test on Flexiglass
Bug: 382477212
Flag: com.android.systemui.scene_container
Change-Id: I1ccd6590867d8849b01cebf2d9dc1bcceb6d57f7