Fix ActivityRecord#attachCrossProfileAppsThumbnailAnimation issue

Since Cross-Profile app thumbnail animation is an transparent animation
layer which should be above SnapShotStartWindow (attached in
ActivityRecord), and the layer should be attached in its root task.

Also, use getRelativeFrameLw to get relative position of its parent for
thumbnail surface.

Fix: 149692548
Test: manual as below steps:
1. Create a work profile (e.g. via TestDPC - go/testdpc)
2. Launch a personal app that supports the CrossProfileApps API (e.g. Gmail),
   ensuring that said app is also installed in the work profile
3. Tap "Switch to work profile"
Expecting Profile switching animation background to be semi-transparent

Change-Id: Ib19f669fac891f1d9d7aa765db89538057dd6318