Updated icon and text font as well as scrim values to make the text and
icon visible in both themes and different wallpapers.
Fix: 408437743
Test: Go to overview in empty state(no tasks)
Flag: com.android.launcher3.enable_overview_background_wallpaper_blur
Change-Id: Ic76d25f4a70bffa402950fc4c3c3fade32c66c2b
