Fix kotlin nullable errors in frameworks/libs/systemui

Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.

Bug: 294110802
Test: builds
Change-Id: If8dc1d32d7fd02e41c12cfb1571374c1e974e87c
Merged-In: If8dc1d32d7fd02e41c12cfb1571374c1e974e87c
4 files changed
tree: 1e55e142ec3bec78e08830866c43f6d09d0ab7f6
  1. animationlib/
  2. iconloaderlib/
  3. motiontoollib/
  4. viewcapturelib/