Iterating on stack layout

- Tweaking initial layout to show more of the next task
- Bounding the width of the stack to the smallest display edge length
- Fixing issue where the screen pinning button was not shown when
  entering recents from home, and the task view clip state was not
  restored correctly for tasks in front of the launch task.
- Fixing issue where there was no alpha during the transition to/from
  home
- Refactoring and removing unused dimens, and moved remaining layout
  calculation logic out of RecentsConfiguration.
- Fixing small regression in finding task anchor scroll points. This
  caused tasks to be animated strangely when swiping to dismiss and
  the task had an override task progress.
- Fixing several regressions in drag and drop due to override progresses

Change-Id: I1eac1dcea19e502bc7fe6362011b38977e3f3d6d