Point Cloud System: Add getters

[Popov72]

It can come in handy to get the position/colors/uvs of the particles generated by the point cloud system so I have added some getters.

[azure-pipelines]

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.

[azure-pipelines]

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