Add system property to enable/disable fling to dismiss for PiP and Bubbles.

This will prevent the users from accidentally dismissing the pip when flinging
quickly towards the dismiss target. The dismiss action will now require an
intentional drag over the dismiss target.

Default value for both properties maintains the original dismiss behavior.

Bug: 214264312
Test: manually, set the property to false, open pip, move it up, fast fling
towards dismiss target -> pip remains on screen, similar for bubbles

Change-Id: I95cbbcbd3f15e5ab5ab708ecfa91f86c26fa3024