Update TaskView corner radius dynamically

Previously we set the corner radius just once when TaskView is
constructed, but this doesn't work when reusing the TaskView on a
different display that has a different corner radius.

Flag: none
Test: FullScreenDrawParamsTest
Test: kill launcher, open Overview on one display, then switch to
another display with different corner radii and ensure task radii
have updated while quick switching
Fixes: 293224095

Change-Id: I5f0697a4697400ec0e003c116774d74a945ee59e