GH-77757
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Validate extension JSON: Error: Field 'classes/Viewport/methods/gui_get_focus_owner': is_const changed value in new API, from false to true.
Validate extension JSON: Error: Hash changed for 'classes/Viewport/methods/gui_get_focus_owner', from 31757941 to A5E188F5. This means that the function has changed and no compatibility function was provided.

This method does not affect the state of Viewport so it should be const.
