Slider's increase and decrease buttons should not be focusable

[martintabakov]

Bug report

When the Slider's increase and decrease buttons should not be focusable.

Reproduction of the problem

1. Open the Keyboard Navigation demo - https://demos.telerik.com/kendo-ui/slider/keyboard-navigation
2. Focus the Decrease button
3. Try pressing space/enter key

Current behavior

The Slider's value cannot be changed through the keyboard when the buttons are focused

Expected/desired behavior

Increase and Decrease buttons should not be focusable. They should have tabindex -1 and aria-hidden attribute, following the Slider aria spec. Slider's keyboard navigation is described in the Keyboard spec.
Clicking on Increase/Decrease button should focus the draghandle of the Slider

Environment

• Kendo UI version: 2024.1.319
• Browser: [all]