[NUI] Add public types to replace nested types of Components.Slider (#1808)

[NUI] Add public types to replace nested types of Components.Slider (#1808)

To replace nested types (CA1034 of StyleCop), the followings are added.
- class SliderValueChangedEventArgs
- class SliderSlidingFinishedEventArgs
- event EventHandler<SliderValueChangedEventArgs> in Slider class
- event EventHandler<SliderSlidingFinishedEventArgs> in Slider class

The followings are deprecated.
- class ValueChangedArgs in Slider class
- class SlidingFinishedArgs in Slider class
- event EventHandler<ValueChangedArgs> in Slider class
- event EventHandler<SlidingFinishedArgs> in Slider class

Co-authored-by: Jaehyun Cho <jae_hyun.cho@samsung.com>