chart.js: Update ChartData to accept both Arrays and ReadonlyArrays (#42023)

By changing the types for `ChartData["labels"]` and `ChartData["datasets"]`
to ReadonlyArrays we can pass either ReadonlyArrays or Arrays as ChartData.

This is useful when chart.js is used inside a React component where the
props are readonly.

types/chart.js/chart.js-tests.ts

@@ -411,6 +411,15 @@ if (doughnutChart.getDatasetMeta(0).data.length > 0) {
     console.log(doughnutChartView.y);
 }
 
+// Passing readonly data as ChartData
+const readonlyDataInput: {
+    labels: ReadonlyArray<string>;
+    datasets: ReadonlyArray<{
+        data: number[];
+    }>;
+} = { labels: [], datasets: [] };
+const readonlyData: Chart.ChartData = readonlyDataInput;
+
 // Time Cartesian Axis
 const timeAxisChartData: Chart.ChartData = {
     datasets: [{

types/chart.js/index.d.ts

@@ -243,8 +243,8 @@ declare namespace Chart {
     }
 
     interface ChartData {
-        labels?: Array<string | string[] | number | number[] | Date | Date[] | Moment | Moment[]>;
-        datasets?: ChartDataSets[];
+        labels?: ReadonlyArray<string | ReadonlyArray<string> | number | ReadonlyArray<number> | Date | ReadonlyArray<Date> | Moment | ReadonlyArray<Moment>>;
+        datasets?: ReadonlyArray<ChartDataSets>;
     }
 
     interface RadialChartOptions extends ChartOptions {