Examples: Add viewportSafeUV in webgpu_backdrop

[sunag]

Related issue: #29025

Description

Improve the example and add good practices.

[wcandillon]

@sunag when using this new node, I am getting the following validation error:

Validation: Source [Texture (unlabeled 393x754 px, TextureFormat::Depth24Plus)] sample count (4) and destination [Texture (unlabeled 393x754 px, TextureFormat::Depth24Plus)] sample count (1) does not match.

Any chance you could help find the underlying API call and maybe root cause of the issue? I would love to debug this further.

[wcandillon]

The issue might be on our side but I am wondering if you could set me in the right direction

[sunag]

WebGPU needs specific methods to deal with sampled textures and this has not been implemented yet, WebGPURenderer( { antialias: false } ) will help solve these issues until we improve this support.

[wcandillon]

thank you for providing this context, appreciate it :)