Adds an event handler that runs when the element is clicked.
An element receives a click event when a user clicks on the element and releases.
When a user double-clicks an element, two click events are fired.
Note: Do not use the Editor Link panel to redirect on click when a link is already
defined using the onClick() function. To avoid unpredictable behavior, remove
the link from the Editor Link panel.
handler(event: MouseEvent): void The name of the function or
the function expression to run when the element is clicked.