Introduce `hasTaskViews()` to RecentsView

- This function is going to replace all the call sites that compares
  `getTaskVieCount()` and `0`.
- This is based on the fact that this count can not be a negative
  number.
- Introduce `getLastTaskView()` to get the last TaskView inside the
  RecentsView.

Flag: EXEMPT as no functionality changes
Bug: 379942019
Test: Manual
Change-Id: Iefb107d1aba61549a870f14c18e025c34b19a1b5