Capture screenshot when animating to home

This is to ensure the task thumbnail is captured in the correct
orientation, rather than waiting until after the task pauses
which might be after the device rotates to portrait.

Also update the state to wait until screenshot is captured
before finishing the transition to home.

Test: testStressPressHome
Test: Swipe up from a forced landscape app, enter overview;
      ensure task view thumbnail is shown correctly

Bug: 132687470
Change-Id: I5cd5f4b2a413628a8bdcb456e2d132c1c2da5258