Add OverviewScrim to show below overview but above workspace

- Refactor some basic scrim logic to Scrim class and have
  WorkspaceAndHotseatScrim and OverviewScrim extend it
- Draw OverviewScrim under recents unless predictions are disabled, in
  which case draw it under hotseat (since that is in recents)
- Remove sysui scrim (behind status bar and nav bar) when overview is
  peeking

Bug: 132455160
Change-Id: Ia5d6f54582a4c5a70e3b2d4a98281567edd68519
diff --git a/src/com/android/launcher3/LauncherState.java b/src/com/android/launcher3/LauncherState.java
index dcfd272..6e2626b 100644
--- a/src/com/android/launcher3/LauncherState.java
+++ b/src/com/android/launcher3/LauncherState.java
@@ -243,6 +243,10 @@
         return 0;
     }
 
+    public float getOverviewScrimAlpha(Launcher launcher) {
+        return 0;
+    }
+
     public String getDescription(Launcher launcher) {
         return launcher.getWorkspace().getCurrentPageDescription();
     }