Set event.sourceEvent in ExecuteCodeAction callback for pointer triggers

[docEdub]

When an ExecuteCodeAction is created with a pointer trigger, the callback's ActionEvent.sourceEvent member is set to undefined.

This change sets the callback's ActionEvent.sourceEvent member to the original event causing the action to be triggered.

Requested on forum: https://forum.babylonjs.com/t/action-enhancements/38043.

[bjsplat]

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[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

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