Increase size of top app in 10:90 vertical split

In the vertical 10:90 layout (flexible split only), the status bar interferes with the (already-small) touch target. So we make the snap point slightly lower to compensate. This does not affect any other layout in flex split or non-flex split.

Bug: 383626044
Flag: com.android.wm.shell.enable_flexible_two_app_split
Test: Top app is bigger on all vertical splits (small and large screen). Other layouts are not affected.
Change-Id: I860d0b6af810946b39a28900151513e084ca35e6