[NUI] Fix scrollableBase focus issue. (#4340)

[NUI] Fix scrollableBase focus issue. (#4340)

* [NUI] Fix scrollableBase focus issue.

fix several issue on focus of scrollableBase.

1. fix wrong focus fallback when next focused children is invisble.
- if current focused object is children of scrollableBase,
  keep focus to current focused object.
- if current focused object is out of scrollableBase,
  to keep focus within the scrollableBase, set focus on scrollableBase.

2. fix wrong next focus returns on next find failed case.
   if next focus find is failed, we can move scroll when key can move
   foward and backward only not other directions.
   In other direction inputs, escape the scrollableBase.

3. fix wrong escape condition of EOS(end of scroll).
   we escape scrollableBase in EOS, but we need to reached EOS firstly,
   and escape scrollableBase on next key input to move out.

4. add conditional debugging log.

5. fix focus samples.
   add text label for notify prev/current focused object.
   fix title of items.
   make padding longer on items.

* [NUI] fix samples.

* [NUI] return null as nextFocusedView will always null.

* [NUI] Update scrollableBase focus logic for missing cases.

* [NUI] Update scrollableBase focus to find next focus properly.

* [NUI] remove unreachable code.