base

Improve peek behavior and fix a few bugs in PanelView

- A single tap on the bar peeks and then dismisses it a again.
- Wait for the peek until the layout has happened.
- Add logic to only peek if user is not flinging.
- Fix a few bugs with panel holes (onExpandingStarted/Finished not
  called correctly.

Bug: 15856091
Bug: 15407838
Bug: 15942322

Change-Id: I1aedf9d01bc8db3d7fed7cea6e341b0be18a8bd9