Flexible 2-app split: Motion and Overview

This CL further polishes flexible 2-app split:
- The offscreen split ratio now properly sits at 10:90
- Animation timings and interpolators are correct to latest POR
- Overview tile now shows correct ratio

Further work:
- Status bar insets are still not respected when app is offscreen.
- The UX guidelines are for flexible split to disregard insets in most scenarios, except in certain cases like pinned Taskbar. More work/clarification is needed there.
- There is a bug where the "swipe up to Overview" gesture is granting momentary focus to the swiped-over window, which I think is not supposed to happen. This is triggering the flexible split motion in some cases and causing a bad UI state.

Bug: 349828130
Test: When flag is off, behavior is unchanged and continues to pass tests
Flag: com.android.wm.shell.enable_flexible_two_app_split
Change-Id: I6e3c2285b6d20b55c529bcdcd23b5b0eaaddefaf