Revert "Trebuchet: Remove workspaceStatusBarScrim"

This reverts commit 147d648f.

Reason for revert: <Removing workspaceStatusBarScrim makes the status bar invisible (white text and icons on white background) when using wallpapers with mostly white color on the top part of the image (when it doesn't activate the light theme with dark text).>

Change-Id: I0dee7f8d64be934b3d445fb3e89564e5c93926df