Slider - new features (#2248)

* Slider - add initial range values

* Slider - adding 'reset' option

* Adding new props to api.json

* Slider - add 'useGap' prop to have the option for the two thumbs to overlap

* Thumb - revert type change

* GadientSlider - reset

* fix initial call for onRangeChange

* fix - reset min only for useRange

* Update demo/src/screens/componentScreens/SliderScreen.tsx

Co-authored-by: Lidor Dafna <66782556+lidord-wix@users.noreply.github.com>

Co-authored-by: Lidor Dafna <66782556+lidord-wix@users.noreply.github.com>

Author: Inbal-Tish