PBR debug visualisations

[superdump]

Objective

• Enable visualisation of PBR and vertex data for debugging purposes
• Fixes Add PBR debug render modes #4235 .

Solution

• Add PbrDebug enum resource covering a bunch of cases
• Use this resource to configure the desired debug visualisation through shader defs, defaulting to PbrDebug::None
• Implement debug visualisations for all the modes in the enum
• Fix clustered forward debug visualisation along the way
• Add a method to be able to invalidate the SpecializedMeshPipelines mesh and vertex layout caches that map from mesh and vertex layouts to specialised render pipelines. This is necessary as the PbrDebug lives outside of and affects all pipelines. Or at least all PBR pipelines, but this was a simple approach.
• Press v in the scene_viewer tool to cycle through the PBR debug visualisations

Normal-mapped normals:

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Changelog

• Added: PbrDebug resource to control debug visualizations.

[IceSentry]

Couple of nitpicks, but otherwise I really like this.

[superdump]

bors try

[bors]

try

Build failed:

• check-doc

[JMS55]

I haven't reviewed this deeply, but I don't see anything about tonemapping in this PR. Some of these modes should maybe disable tonemapping, as we want to see the raw output without adjustments.

[IceSentry]

Yeah, tonemapping didn't exist when this PR was created.

[NthTensor]

This appears to have gone stale and perhaps needs significant rewrites. I propose we close this an open an issue for the feature/adoption.

[NthTensor]

Closing as stale, existing issue suffices. Feel free to re-open Rob, this looked really neat.