fix(slider): improve accessibility by correcting ARIA attributes and tab index - 18.1.x

[georgianastasov]

Closes #14262

The slider control element now follows ARIA guidelines, including:

• tabindex correct 0 value, ensuring the thumb components are correctly focusable within the tab order.
• role set to slider for the thumbs focusable elements.
• aria-valuenow for the current slider value, aria-valuemin for the minimum value, and aria-valuemax for the maximum value.
• aria-valuetext is used when the current value is not user-friendly (e.g., converting numeric values to readable text).
• aria-label is used to provide accessible labeling.
• aria-orientation is set to "horizontal" by default.
• aria-disabled to the thumb components when they are disabled to indicate the element's state.

The slider thumb component has been updated to follow ARIA accessibility guidelines as per WAI-ARIA slider pattern and the implementations outlined in the IgniteUI Web Components Slider specification.

Additional information (check all that apply):

• Bug fix
• New functionality
• Documentation
• Demos
• CI/CD

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them