[XR] fix the samples returned when using multiview in WebXR

[RaananW]

When using multiview on WebXR I don't want to update the samples using setSamples because of the extra work done there (that is not needed).
This is one solution. A different one would be to introduce a (hidden) setter to the _samples of the wrapper but this approach makes sure the state of the wrapper doesn't change.

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[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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