Issue #2943952 by andileco: Enable stacking

charts.module

modules/charts_blocks/src/Plugin/Block/ChartsBlock.php

modules/charts_blocks/templates/charts-block.html.twig

...s/charts_highcharts/src/Charts/HighchartsChartsRender.php

modules/charts_highcharts/src/Plugin/chart/Highchart.php

...ighcharts/src/Settings/Highcharts/PlotOptionsStacking.php

src/Plugin/views/style/ChartsPluginStyleChart.php

templates/views-view-charts.html.twig