[FIX] ts: fix compiling of .d.ts files

It wasn't possible to compile the lib into `.d.ts` since 8a02a6b,
error `... exported class expression may not be private or protected`.[1]

It seems that we cannot have an anonymous class with private/protected
methods. We had a similar issue with the `PivotPresentationLayer`.

This commit adds explicit typing to the functions generating the
funnel chart classes, so typescript doesn't try to infer types for them.

[1]: see microsoft/TypeScript#30355
or microsoft/TypeScript#36060

Task: 0

Author: hokolomopo

src/components/figures/chart/chartJs/chartjs_funnel_chart.ts

@@ -1,13 +1,20 @@
 import {
+  BarController,
   BarControllerChartOptions,
   BarControllerDatasetOptions,
   BarElement,
   CartesianParsedData,
   CartesianScaleTypeRegistry,
+  Chart,
+  ChartComponent,
   TooltipPositionerFunction,
 } from "chart.js";
+import { AnyObject } from "chart.js/dist/types/basic";
 
-export function getFunnelChartController() {
+export function getFunnelChartController(): ChartComponent & {
+  prototype: BarController;
+  new (chart: Chart, datasetIndex: number): BarController;
+} {
   return class FunnelChartController extends window.Chart?.BarController {
     static id = "funnel";
     static defaults = {
@@ -37,7 +44,10 @@ export function getFunnelChartController() {
   };
 }
 
-export function getFunnelChartElement() {
+export function getFunnelChartElement(): ChartComponent & {
+  prototype: BarElement;
+  new (cfg: AnyObject): BarElement;
+} {
   /**
    * Similar to a bar chart element, but it's a trapezoid rather than a rectangle. The top is of width
    * `width`, and the bottom is of width `nextElementWidth`.