Draggable Tests: Fix several whitespace issues.
Core: provide "includeHidden" parameter in $.ui.scrollParent

Even though the user is unable to scroll via the UI, authors
may have custom scrollbars that programmatically set scrollTop.
Therefore, overflow:hidden can be considered a scrollParent.
Draggable: consider offsets from overflow:hidden parents

Developers can programmatically set scrollTop/Left on
draggable containers that are overflow:hidden. They must
be considered for positioning.

Fixes #10147
Draggable: clean up whitespace in scroll option
Draggable: ignore overflow:hidden containers with scroll option

While it is true that overflow:hidden elements can be scrolled
programatically, this breaks user expectation. Therefore, do not
 scroll inside an overflow:hidden container.