[RESTRICT AUTOMERGE] Dimming on an embedded TaskFragment vs. parent Task

Migrate the dimmer to TaskFragment and the dim surface
needs to be offset relative to its parent task.

Bug: 202379687
Test: verify dim in two pane
Change-Id: I95fe47ebc66d419b42c1da8cc8216773c295f1d1
(cherry picked from commit 9b5881335df9095d91b6760f3f459e6e6a3bdda8)
2 files changed