The clear button <button class="mw-ui-icon mw-ui-icon-mf-clear mw-ui-icon-element mw-ui-icon-small clear" title="" style="">Clear</button> doesn't provide values of screenreader users.
It adds to navigation steps needed to search and deleting an input's value is simpler done without this button being exposed for those.

Expected result:
Should be hidden to AT users by adding aria-hidden="true"

Developer notes

It should be possible to pass an option to the Icon element that adds the attribute aria-hidden.
We could add a generic solution (e.g. allow an array of attributes to be added to the parent element) or a bespoke option for the aria-hidden option.

I guess it should default to hidden, unless explicitly stated otherwise.