Add aria label prop for clear button in Searchbox

[Hugodol]

Pull request checklist

• Addresses an existing issue: Fixes #0000
• [ x] Include a change request file using $ npm run change

Description of changes

Added a prop to Searchbocx called clearButtonAriaLabel to add an aria-label to the clear search box button.

Focus areas to test

Added clearButtonAriaLabel to SearchBox.Small.Example for testing.

[msftclas]

All CLA requirements met.

[manishgarg1]

Hi @Hugodol, this (#3946) pull request is trying to achieve the same end goal. Would you be ok if we rejected your pull request and got the other to merge as his change is adding two aria props which you may also need?

[manishgarg1]

Hi @Hugodol, this (#3946) pull request is already merged. It should solve your problem, please reactivate this pull request. thanx.