Add stacking options for Google Charts

modules/charts_google/src/Charts/GoogleChartsRender.php

modules/charts_google/src/Plugin/chart/GoogleCharts.php

modules/charts_google/src/Settings/Google/GoogleOptions.php

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

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

...s_highcharts/src/Settings/Highcharts/ExportingOptions.php

.../charts_highcharts/src/Settings/Highcharts/Highcharts.php

src/Plugin/views/style/ChartsPluginStyleChart.php