Add WebGPU texture-format-tier1, texture-format-tier2, and primitive-index features

[mvaligursky]

Adds support for new WebGPU features:

• Request texture-format-tier1 and texture-format-tier2 GPU features for extended texture format support
• Request primitive-index feature and expose pcPrimitiveIndex built-in in fragment shaders
• Add supportsPrimitiveIndex public property to GraphicsDevice
• Add CAPS_PRIMITIVE_INDEX shader define when the feature is supported
• Reorder WGSL shader assembly to place defines before preamble chunks (order matches WebGL now)

When primitive-index is supported, fragment shaders can access pcPrimitiveIndex which uniquely identifies the current primitive being processed.

based on https://developer.chrome.com/blog/new-in-webgpu-142