GH-115799
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Validate extension JSON: Error: Field 'classes/RenderingServer/methods/viewport_set_size/arguments': size changed value in new API, from 3 to 4.

Optional argument added. Compatibility method registered.

Validate extension JSON: Error: Field 'classes/Viewport/methods/is_using_xr': is_const changed value in new API, from false to true.

Changed to const. Compatibility method registered.
