Draggable: Ensure correct widget removes helper in connectToSortable
Draggable: Ensure css is always restored after connectToSortable drag

Fixes #9675
Draggable: Ensure sortable revert still works after draggable is removed

Fixes #9481
Draggable: Clarify comments and whitespace in connectToSortable
Draggable: Refresh sortables when draggable is added or removed

Since a sortable grows or shrinks when a draggable element is added
to it, refresh the cached positions of sortables whenever an element
is added or removed from the sortable.

Refs #9675
Draggable: Whitespace and naming cleanup of connectToSortable
Sortable: cancelHelperRemoval only considers helper, not placeholder

Refs #9675
Draggable: Add battery of tests to cover connectToSortable

Refs #9481
Refs #9675
Closes gh-1323