Focus running task in overview grid

- calculateTaskSize now returns the Rect for focused task
- Introduced calculateGridTaskSize for non-focused task, and translate non-focused tasks to fit the grid
- As Task Rect is now vertically centered, removed ClearAllButton's grid vertical translation
- When ClearAllButton is not shown (e.g. quickswitch), make sure ClearAllButton's scroll won't be used when page snapping. This happens when page scrolls are translated so they're negative.
- Added back ActionsView when task is focused below the TaskView, which become invisible as you scroll
- In Modal state, move the ActionsView down so it won't cover the TaskView

Bug: 175939487
Test: manual
Change-Id: Idfa94a51f856418adc0503cf04211dcb4b1814fe