[combo-box] Field should not be focused on helper click

[web-padawan]

Description

Originally reported at #2232 (comment)

The click event listener on the combo-box causes it to be focused regardless of where the user clicked:

web-components/packages/combo-box/src/vaadin-combo-box-mixin.js

Line 285 in 8a89320

this.addEventListener('click', this._boundOnClick);

Expected outcome

Click on helper text should not focus the field, as in other components e.g. vaadin-select.

Actual outcome

Clicking the helper text focuses the combo-box input and opens the dropdown.

Environment

• v22 and v23