Enables drag to dismiss for PiP and adds a dark scrim when dismissing

- Adds a scrim that fades in as the PiP is dragged past the bottom movement
  bounds.
- Tweaks the values for minimizing the PiP and dismissing the PiP
- Fixes an issue where the PiP could be minimized in the bottom corners
  of the screen

Test: Manual - drag PiP to bottom of screen to dismiss or swipe down on
PiP when it's at the bottom of the screen
Bug: 35358768
Bug: 35358628
Change-Id: Ib4ad5ed7094fef76ea979b46ea7e03d746625d00

core/java/com/android/internal/policy/PipSnapAlgorithm.java

@@ -321,7 +321,7 @@ public class PipSnapAlgorithm {
                 stackBounds.top));
         boundsOut.set(stackBounds);
         if (mIsMinimized) {
-            boundsOut.offsetTo(boundedLeft, boundsOut.top);
+            boundsOut.offsetTo(boundedLeft, boundedTop);
             return;
         }