Introduce TaskView.setObscuredTouchRegion.

- We have the existing api TaskView.setObsucredTouchRect(), but introduce new api to provide more flexibility.
- go/aaos-taskview-improvements

Bug: 225388469
Test: Check the behavior in the sample app with 2 buttons.
Change-Id: I3db7fcc45b73523fb17039f5a88d015cefce4819