Simplify UI and animation choreography a bit

A number of changes to improve the robustness of the
startup/reset/dismiss process of the screenshot UI.

Brief summary:

Use visibility=invisible always for preview image
Wait for pre-draw to start animation
Apply initial config to "interesting changes" tracker
Rename: mOnCompleteAction -> mOnDismissedAction
Rease more resources earlier at shutdown
Remove some uneccessary main thread deferrals
resetScreenshotView -> finishDismiss
Resolve some cases where reset is called multiple times on exit
Update window token usage and apply to scroll capture at window attach
Simplified animation parameters, coordinate systems, etc.

Bug: 174509231
Bug: 174682382
Test: manual; take a screenshot, dismiss, share, edit, swipe away
Test: manual; open overview, tap screenshot

Change-Id: I3b84da3592970ac5c2a5eb34326eabaef003993f