Add mechanism for customization of rounded corner insets

TaskBar and divider bar now draw fake rounded corners. We need a way to
report these fake rounded corners instead of the real ones.

1. A new field providedInternalTaskBarInsets is added in
   WindowManager.Params for task bar(Launcher) to set.
   - Set this field to the task bar height(not including rounded
     corner height) when task bar is expanded.
   - Set to 0 when task bar is stashed
2. A ned field mRoundedCornerFrame is added in InsetsState.
   - The frame that rounded corners are relative to.
   - It's used to re-calculate the fake rounded corners.
3. In WindowState.getInsetsState(), check below condition:
   - It's a task
   - The task bar insets is not empty
   - In split screen
   If all conditions are met, we use task bounds as new frame to
   calculate rounded corners instead of display frame.
4. A new method RoundedCorners.insetsWithFrame() is added to handle such
   case.

Bug: 196387239
Test: atest RoundedCornersTest

Change-Id: Icd6d39bd8cf6534531f7bbb209296785b76891db