feat: add drag&drop support to vaadin-chart

[bwajtr]

Description

Until now, the vaadin-chart component did not support drag&drop at all.

This PR brings support for drag and drop:

• It loads the required extension module
• It adds three new events to the vaadin-chart: dragStart, drag and drop -> the code is the same as for any other chart point event

The only significant change is in the __createEventListeners method: I found during testing, that the data of the customEvent are not correct in case of dragStart. Highcharts fires dragStart with a different content of the event object: event.type is missing, and the event object itself is actually the original mousedown event object.
However, Highcharts passes the point that is being dragged as a this of the event handler (it does this for every event type... even for the series events - in that case this refers to the series). Therefore the change in the __createEventListeners -> the arrow function was changed to a regular function, so different this can be passed to it. We then set this to customEvent.detail.point as the point that is being dragged.

I added a test that simulates what happens when you click the chart and you are over the draggable point.

Part of vaadin/flow-components#4731

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/contributing/pr
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.
• I have not completed some of the steps above and my pull request can be closed immediately.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud