MeshPhongMaterial: Add support for scene.environment IBL.

[mrdoob]

Description:

Adds image-based lighting (IBL) support to MeshPhongMaterial, allowing it to receive indirect diffuse lighting from scene.environment. This follows the same pattern as the recent MeshLambertMaterial implementation.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	356.13 84.63	356.54 84.66	+404 B +29 B
WebGPU	621.5 172.57	621.5 172.57	+0 B +0 B
WebGPU Nodes	620.1 172.33	620.1 172.33	+0 B +0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	488.37 119.53	488.78 119.56	+404 B +26 B
WebGPU	692.03 187.86	692.1 187.86	+62 B +4 B
WebGPU Nodes	641.77 175.02	641.77 175.02	+0 B +0 B