WebGPU support to shadow atlas (shadow cascades + clustered shadows)

[mvaligursky]

• shadow shaders updated to work with WebGPU
• added a private way to display unfiltered texture for debugging, such as shadow map (WebGPU only) - this involved supporting multiple samplers per texture.
• handling renderTarget.flipY when rendering using a viewport (shadow atlas) by flipping viewport as well on WebGPU
• using WebGPU error scopes to report bind group validation errors with additional relevant data (used descriptors ...) to considerably improve understanding of those errors. To be used to validate other WeGPU APIs in the future. Based on https://toji.dev/webgpu-best-practices/error-handling

Missing for full support of clustered shadows:

• support to clear only part of the render target (viewport) - WebGPU does not have a clear function to do this, and it needs to be implemented using a quad draw. Separate PR. This is to handle a case where not all shadows are updated per frame, and so the whole render target cannot get cleared.

clustered-shadows.mov

[willeastcott]

Approving with minor feedback...