Fix the jelly effect when scrolling the a11y floating menu.

Root cause:
The default scroll mode of RecyclerView is scrollable.

Solution:
Set OVER_SCROLL_ALWAYS when the actual height of target list exceed the
available height, otherwise OVER_SCROLL_NEVER.

Bug: 184817161
Test: atest AccessibilityFloatingMenuViewTest
Change-Id: I9a2bfd674141475e5546b1ed5450e65132ffd384