fix: only drain WGSL shader include loaders for WGSL effects

LoadPendingIncludesAsync was called unconditionally in effect.ts for all
effects. In the CDN bundle, all WGSL shader modules execute at load time and
push their include loaders to _PendingIncludesLoaders. The first GLSL/WebGL
effect created would then drain the entire WGSL loader queue before proceeding,
stalling shader initialization until hundreds of dynamic imports resolved.
This caused visual timing regressions in 24 WebGL2 visualization tests.

Fix: gate the call on ShaderLanguage.WGSL so only WGSL effects process the
include queue. GLSL effects still get LoadPendingIncludesAsync via their
extraInitializationsAsync callback (in each material's shader loading code)
for any WGSL includes that happen to be pending at that point.

Author: RaananW

packages/dev/core/src/Materials/effect.ts

@@ -427,10 +427,15 @@ export class Effect implements IDisposable {
             await extraInitializationsAsync();
         }
 
-        // Eagerly load all pending shader includes so that ProcessIncludes is synchronous.
-        // The WGSL processor is a singleton that stores per-effect state; async include resolution
-        // would allow another effect's Initialize() to overwrite that state mid-processing.
-        await EngineShaderStore.LoadPendingIncludesAsync();
+        // For WGSL effects, eagerly load all pending shader includes so that ProcessIncludes
+        // is synchronous. The WGSL processor is a singleton that stores per-effect state;
+        // async include resolution would allow another effect's Initialize() to overwrite
+        // that state mid-processing. GLSL effects do not use _PendingIncludesLoaders and
+        // must not drain the WGSL queue (which stalls the first GLSL effect until all WGSL
+        // includes have resolved, causing visual timing regressions in tests).
+        if (this._shaderLanguage === ShaderLanguage.WGSL) {
+            await EngineShaderStore.LoadPendingIncludesAsync();
+        }
 
         this._processingContext = shaderProcessingContext || this._engine._getShaderProcessingContext(this._shaderLanguage, false);