Draw the workspace scrim in the LauncherRootView instead of DragLayer

=> The entire DragLayer is translated during the -1 transition which creates a janky looking edge at the top of the screen

=> By bumping the scrim up a level, we avoid this

=> Separated WorkspaceAndHotseatScrim into two separate scrims, since only part of the scrim needed to be bumped up to a level. Further, it was an overloaded class.

=> We had previously been implicitly relying on the fact that the scrim was rendered in the Workspace parent; we need to make sure to propagate workspace inavlidations to the container of the scrim. While things would still work without this change, it's more correct to leave it, as we no longer assume a hierarchy for functinoality.

Bug: 178215332

Test: manual verification. See video in bug.

Change-Id: I0a76ddf35ceea8c9635367f69380ef24f42e9479