Revert "Filterable: Changed the default of option hidedividers to true. Fixes #6261."

This reverts commit cd4af5d3f18a276003b47a7be8602b3514cfb191.
Filterable: Backcompat: Turn on hidedividers when the child widget turns out to be a listview in order to reproduce 1.3.x behaviour. Fixes #6261.