Don't draw task insets or corners in multi window mode

Test (all in multi window and non-multi window):
- Quick switch from home screen
- Quick switch from an app
- Swipe up from an app (slowly)
- Swipe down on a task (slowly)

Bug: 131689686
Change-Id: I69bf6dd1a34904cdf5ec7febea8f858012e2a0ac