WGSL implementation of VSM shadows

[mvaligursky]

• both blurring as well as sampling VSM shadows were converted to WGSL

[Copilot]

Pull Request Overview

This PR implements the conversion of VSM shadow blurring and sampling from GLSL to WGSL to support WebGPU. Key changes include:

• Refactoring and extracting variable calculations in shadow functions.
• Adapting blur shader code to use placeholder substitution (e.g. {SAMPLES}) and WGSL syntax.
• Adding WGSL shader chunks and updating shader/chunk selection in the shadow renderer.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/scene/shader-lib/chunks/lit/frag/lighting/shadowEVSM.js	Updated to extract variable Z for clarity in getShadowSpotVSM32.
src/scene/shader-lib/chunks/lit/frag/blurVSM.js	Updated uniform and loop expressions to incorporate placeholder {SAMPLES}.
src/scene/shader-lib/chunks-wgsl/lit/frag/lighting/shadowEVSM.js	Added WGSL implementation for EVSM shadow functions.
src/scene/shader-lib/chunks-wgsl/lit/frag/lighting/lightDeclaration.js	Fixed variable declaration syntax by adding the missing colon.
src/scene/shader-lib/chunks-wgsl/lit/frag/blurVSM.js	Introduced WGSL version of the blur VSM shader with WGSL-syntax adaptations.
src/scene/shader-lib/chunks-wgsl/common/vert/fullscreenQuad.js	Added WGSL vertex shader for full-screen quad rendering.
src/scene/shader-lib/chunks-wgsl/chunks-wgsl.js	Updated import and shader chunk exports to include WGSL shaders.
src/scene/renderer/shadow-renderer.js	Modified shader selection and creation to support WGSL with proper attribute mapping.

Comments suppressed due to low confidence (3)

src/scene/shader-lib/chunks/lit/frag/blurVSM.js:8

• Ensure that the placeholder {SAMPLES} is correctly substituted during shader preprocessing for both the uniform declaration and subsequent usage.

uniform float weight[{SAMPLES}];

src/scene/shader-lib/chunks-wgsl/lit/frag/blurVSM.js:22

• Check that accessing the weight array element via '.element' is the intended WGSL syntax; typically, array elements are accessed directly unless a custom type wrapper is used.

moments = moments + c.xyz * uniform.weight[i].element;

src/scene/renderer/shadow-renderer.js:500

• Verify that using '{SAMPLES}' as a placeholder in the shader code is processed correctly by the shader preprocessor and is consistent with the usage in other shader files.

let blurFS = `#define {SAMPLES} ${filterSize}\n`;