Set alpha to 1 if not using alpha animation

For multi-activity PiP a new task is created, which triggers TO_FRONT
transition request that sets the alpha to 0. Since we are using bounds
animation in 3 button nav on Home press, we need to reset that alpha
to be 1 again.

Bug: 286183129
Test: manually, see http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/cQ7FF3EarUUS2W14W9M806
Change-Id: I197de8d24186850e76eb1ec5ee7a713079ff109e

libs/WindowManager/Shell/src/com/android/wm/shell/pip/PipTransition.java

@@ -856,6 +856,9 @@ public class PipTransition extends PipTransitionController {
         final int enterAnimationType = mEnterAnimationType;
         if (enterAnimationType == ANIM_TYPE_ALPHA) {
             startTransaction.setAlpha(leash, 0f);
+        } else {
+            // set alpha to 1, because for multi-activity PiP it will create a new task with alpha 0
+            startTransaction.setAlpha(leash, 1f);
         }
         startTransaction.apply();