Steps to reproduce (assumes ChromeVox or similar)

1. Open https://elastic.github.io/eui/#/guidelines/buttons in a new tab.
2. Tab through the navigation to the main content pane.
3. Tab down to the first icon button example

Actual Result

Several buttons with several different icons read the incorrect aria-label "Next"

Expected Result

The aria-label is set correctly to match the icon)

Suggested Fix
Review the component code to make sure the right label is applied to match the icon.

Category: #688: Elastic UI Buttons Accessibility
Relevant WCAG Criteria: 2.4.4 Link Purpose (In Context)