feature request: extend NO_SCROLLBAR with horizontal/vertical options

Sometimes a scrollbar can appear that has no effect because it scrolls 0px in that direction. The same is true for very small "scrollable distances" like a couple of pixels.

Thus it would be nice to be able to disable just one of the scrollbars and keep the other if the content inside is big enough to require it.

Start by locating the NO_SCROLLBAR implementation and the code that determines horizontal and vertical scrollable distances. Check how zero or very small distances currently produce scrollbars. Done means supporting independent horizontal and vertical disabling while retaining a scrollbar when the other direction needs it.

Written by the indexing model from the issue text.