TargetCamera: Add Node Constructor code for TargetCamera

[PolygonalSun]

This PR contains a simple fix for an issue found in a forum post. When a .babylon file is created with a TargetCamera and reimported, the camera will imported using the default behavior (creating a UniversalCamera). The fix here is to add a NodeConstructor to handle instances of TargetCameras

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[bjsplat]

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Visualization tests for WebGPU (Experimental)
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