WebGPUPipelineUtils: Fix blending with premultiplied alpha. (#29100)

* WebGPUPipelineUtils: Fix additive blending with premultiplied alpha.

* WebGPUPipelineUtils: Fix normal blending as well.

src/renderers/webgpu/utils/WebGPUPipelineUtils.js

@@ -280,11 +280,11 @@ class WebGPUPipelineUtils {
 				switch ( blending ) {
 
 					case NormalBlending:
-						setBlend( GPUBlendFactor.SrcAlpha, GPUBlendFactor.OneMinusSrcAlpha, GPUBlendFactor.One, GPUBlendFactor.OneMinusSrcAlpha );
+						setBlend( GPUBlendFactor.One, GPUBlendFactor.OneMinusSrcAlpha, GPUBlendFactor.One, GPUBlendFactor.OneMinusSrcAlpha );
 						break;
 
 					case AdditiveBlending:
-						setBlend( GPUBlendFactor.SrcAlpha, GPUBlendFactor.One, GPUBlendFactor.One, GPUBlendFactor.One );
+						setBlend( GPUBlendFactor.One, GPUBlendFactor.One, GPUBlendFactor.One, GPUBlendFactor.One );
 						break;
 
 					case SubtractiveBlending: