Allow clipping individual direction of TaskView

- Only clip the nav bar (taskbar), and always do that in tablets regardless of whether taskbar is stashed, so TaskView always have the same ratio (mocks: https://docs.google.com/presentation/d/1_3zQak_C9FzDPCcIdYagfUit4QyqfdRxetkim3dI9rY/edit#slide=id.ge211eb96a5_5_8)
- When taskbar is present, don't use full thumbnail to avoid TaskView resizing in fullscreen: http://dr/file/d/18C8DSygPBU1gkmMQPPIIa2NqQESFurxW/view?resourcekey=0-8W79f31gstzI_1ZPpHulBQ
- When taskbar is stashed, we still need full thumbnail to gradually crop out the taskbar in overview

Test: Open Chrome, swipe up and ensure status bar inset stays in overview but taskbar stays clipped out from the onset.
Bug: 190681228
Change-Id: I9d563572f2e6800e90d567c2bfae4528a126f24e