[PiP2] Update the magnetic target location on show

Update the magnetic magnetic target location on screen
upon dismiss target showing as we are dragging PiP.

This makes sure the target view matches the actual magnetized
area center location.

Bug: 380336325
Flag: com.android.wm.shell.enable_pip2
Test: swipe PiP to home from landscape and drag to dismiss
Change-Id: I08d87dcfda1b3c39e73b4fef1c10fceca14301dc