SSSNode: Add new node for Screen-Space Shadows. (#32050)

* SSSNode: Add new node for Screen-Space Shadows.

* Examples: Use `PCFSoftShadowMap` in SSS demo.

Author: Mugen87

examples/files.json

@@ -426,6 +426,7 @@
 		"webgpu_postprocessing_ssaa",
 		"webgpu_postprocessing_ssgi",
 		"webgpu_postprocessing_ssr",
+		"webgpu_postprocessing_sss",
 		"webgpu_postprocessing_traa",
 		"webgpu_postprocessing_transition",
 		"webgpu_postprocessing",