Feat - itemAnchorClick

[lofcz]

Currently, Muuri always opens <a> hrefs when clicked - we needed a mechanism to do this conditionally. Think Jira-like kanban board where items are represented by <a> elements, and the elements contain a checkbox which prevents opening the href:

To support this, a new option itemAnchorClick is introduced. If set, this handler enables preventing navigation. We use it like:

itemAnchorClick: function(item, event) {

    // if we clicked on the checkbox, stop
    if (event.target.closest('.kanbanCardCheckbox')) {
        event.preventDefault();
        return false;
    }
    
    let id = item.getElement().getAttribute("data-el-id");
    
    // clicked on the item, navigate (Blazor)
    if (id) {
        pars.net["invokeMethodAsync"]("JsAppNavigation", id);
    }
    
    return false; // return true would result in calling "openAnchorHref" as before this PR
}