[Bug][Pager] Disabled buttons are accessible by keyboard

[vveesseelliinnaa]

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• Bug report

Current behavior

Disabled buttons do not have tabindex=-1, so they are accessible by user using tab key.

Expected behavior

Disabled "First", "Previous, "Next" and "Last" links are marked up and announced as disabled and are not keyboard focusable.

Minimal reproduction of the problem with instructions

1. https://www.telerik.com/kendo-react-ui/components/datatools/pager/keyboard-navigation
2. Try to navigate through the disabled buttons of the Pager.
3. Observe that the disabled "First", "Previous, "Next"" and "Last" links are not announced as disabled and receive keyboard focus.

Reported in: 1670296