Scroll capture: Allow scroll views with multiple child views

This change relaxes requirements for detecting a ViewGroup as a
ScrollView. The check for a single child view is removed. The
important aspect is that scrollY is used to move the viewport.

Bug: 189827634
Flag: android.view.flags.scroll_capture_relax_scroll_view_criteria
Test: atest ScrollCaptureInternalTest
Test: Manual - Test Keep note view, using SparseRecyclerView
Change-Id: I831b1ddb4527a27bae9912324d9d4de7dd358362