SF: Reparent for screehshots should only be called on old parent layers

During a reparenting, a parent's children do not change, instead only the child's
reference to its parents change.

Bug: 124389032, 124372894
Test: go/wm-smoke
Test:build and run aosp_cf_x86_pasan
Change-Id: Ibceb036b8927eef143d9e544ac850c7c6379e1fe