On filter handler

@inner
@param {Object} file the template file
@param {string} filterName the filter name
function handleOnFilter(file, filterName) {
    let usedFilters = file.filters;
    usedFilters || (usedFilters = file.filters = []);
    if (!usedFilters.includes(filterName)) {
        usedFilters.push(filterName);
    }
}