ComposedHeaderProvider in ComposedHeaderProvider with sticky

[Banck]

Hello, @lkzhao !
I've noticed that if ComposedHeaderProvider (isSticky == true) has another ComposedHeaderProvider (isSticky == true) then header in the second headerProvider has collection top anchor as stop collision (i.e the header in second headerProvider will be behind the header in first headerProvider), but I think it should be bottom anchor of the header in first headerProvider (i.e the header in second headerProvider will be under the header in first headerProvider)

[Amzd]

The source of this issue is that the layout of a nested provider doesn't get the visible frame inset from the outer provider. To fix this, #102 should be addressed.