ui: Add `show_scrollbar` method to Picker (#25025)

Now, you can pass `show_scrollbar` to Picker that implement a
`uniform_list`. If that's on, the scrollbar should auto-hide if you move
your focus elsewhere. By default, this method is turned off.

Release Notes:

- N/A

---------

Co-authored-by: smit <0xtimsb@gmail.com>