Adjusts Clear all to be vertically centered with the tasks.

I made a sample task where the content of the app was
centered, and I added lines to demonstrate the center
while in Overview. As you can see, the center of the
app content is slightly different from the TaskView
in Recents - it seems part of the bottom of the app
gets removed when transitioning to Recents (for the
rounded corner radius or nav bar?). On Pixel 4, I
had to add 46dp of padding to the bottom line for it
to appear at the bottom of the screenshot in Recents.

Screenshot: https://drive.google.com/file/d/1xzQNXWb0T0UGDhDS9Ov-AduM3nd-pfg8/view?usp=sharing
Before: https://drive.google.com/file/d/1ghN9VWP44XjcZkdmI106dy4_jB4Vs4J3/view?usp=sharing

Rotating between landscape and portrait:
https://drive.google.com/file/d/1OD5aKT9LCE5w950-6AaHfWXU4sLyW3Qe/view?usp=sharing

Fixes: 154964045
Change-Id: I594057e3b5df58c5a907b6ca14daa700d5011b7b