Fixing jumping HUN when starting swiping

HUN was jumping vertically wherever we are using large screen header: all large screen configurations + handheld landscape.
This was caused by different way of calculating appearEnd and appearStart positions. appearEnd was taking into account stack scroller margin introduced by large screen header, but appearStart was just using headsUpInset which ignores that margin. Accounting for margin fixes this issue.

Bug: 259679234
Test: manually, pull down/up on HUN and see it not jumping vertically, videos attached
Change-Id: Ib259d0eda9c80d78d517f018bccc7011dcb4203c