MDL-84398 libraries: Configure locale property for ChartJs

ChartJs has a property called locale that makes possible to format scale
numbers according to a language. This way we ensure that decimal places
will be displayed correctly in the chart labels and tooltips.

lib/amd/src/chart_output_chartjs.js

@@ -200,6 +200,7 @@ define([
                 datasets: this._makeDatasetsConfig()
             },
             options: {
+                locale: document.documentElement.getAttribute('lang'),
                 responsive: true,
                 maintainAspectRatio: false,
                 plugins: {
@@ -307,10 +308,11 @@ define([
     Output.prototype._makeTooltip = function(tooltipItem) {
 
         // Get series and chart data to rebuild the tooltip and add labels.
+        const formatter = new Intl.NumberFormat(this._config.options.locale);
         var series = this._chart.getSeries()[tooltipItem.datasetIndex];
         var serieLabel = series.getLabel();
         var chartData = tooltipItem.dataset.data;
-        var tooltipData = chartData[tooltipItem.dataIndex];
+        var tooltipData = formatter.format(chartData[tooltipItem.dataIndex]);
 
         // Build default tooltip.
         var tooltip = [];