Defines in cube_uv_reflection_fragment can break MeshPhongMaterial

Describe the bug

Short defines such as those in cube_uv_reflection_fragment can clash with user-defined materials via ShaderMaterial and built-in materials that use bsdfs (related: #22728).

To Reproduce

The above behavior can be reproduced when passing a texture from PMREMGenerator to a MeshPhongMaterial via envMap.

Code

import * as THREE from 'three';
import { RGBELoader } from 'three/examples/jsm/loaders/RGBELoader.js';

const renderer = new THREE.WebGLRenderer();

new RGBELoader().load( '/lago_disola_1k.hdr', ( texture ) => {

  const envMap = new THREE.PMREMGenerator( renderer ).fromEquirectangular( texture ).texture;

  const geometry = new THREE.BoxGeometry();
  const material = new THREE.MeshPhongMaterial( { envMap } );
  const mesh = new THREE.Mesh( geometry, material );
  renderer.compile( mesh );

});

Live example

• https://codesandbox.io/s/1b9mv3

Expected behavior

Defines in cube_uv_reflection_fragment should be more specific and probably follow the existing local cubeUV_* pattern.

Screenshots

Platform:

• Device: [N/A]
• OS: [N/A]
• Browser: [N/A]
• Three.js version: [r143, since #18004]

[CodyJasonBennett]

@Mugen87 @mrdoob Please understand that the issue in this PR was caused by the OP using a PMREM with MeshPhongMaterial, which is not supported.

I think this issue is pretty clearly about loose defines made in cube_uv_reflection_fragment which can only cause trouble with built-in materials and user-defined materials – bsdfs being merely an example.

If MeshPhongMaterial (and also MeshLambertMaterial & MeshPhysicalMaterial) aren’t supposed to include cube_uv_reflection_fragment then remove it, but it’s not the (intentional) focus of this issue.

Edit: I see you already got it in #24475

[Mugen87]

and what is the current policy on using a PMREM as a background texture?

Since we want to support background blurriness at some point, the engine potentially needs PMREM support for the background shader. #23712 implemented this feature with normal mipmaps, however, other engines actually use PMREM. So this question has to be decided first before we can update the background shader.