Introduce RecentsView.getTaskViews for easy for-each looping

- This vastly simplified the need to call do a indexed loop with getTaskViewCount() and calls requireTaskViewAt() each time, useful for code that needs to loop all TaskViews
- removeTasksViewsAndClearAllButton and resetTaskVisuals have no reason to loop reversed, so I just loop them in order

Fix: 365534984
Test: presubmit, manual
Flag: EXEMPT REFACTOR
Change-Id: Ib69f8439f3a7509fc57ec2430affa207c038bf46