Editor: Fixed uncaught exception when environment/background combination is illegal

[ycw]

The issues:

1. Currently it causes error when environment is BACKGROUND and background is not TEXTURE|EQUIRECT; If it happens, users have no clue about the failure because the error is only shown in console:

2. Environment will be unlinked from background when recovering from IndexedDB, i.e. environment can never be 'BACKGROUND' after recovering.

This PR fixed 1 by checking If environment/background combination is illegal, then highlight the environment selector in UI

https://github.com/mrdoob/three.js/assets/1063018/4aa0f62a-8166-400d-a767-25859eef1e18

This PR fixed 1 by handling exception of illegal combinations.

This PR fixed 2 by checking if environment.uuid is equal to background.uuid, then set environment value to BACKGROUND

Preview: https://raw.githack.com/ycw/three.js/editor-handle-scene-env-exception/editor/index.html

[Mugen87]

This kind of error highlighting is unusual for the editor. How about we fix issue 1 by silently ignoring invalid input for Scene.environment like so:

case 'Background':

	useBackgroundAsEnvironment = true;

	if ( scene.background !== null && scene.background.isTexture ) {

		scene.environment = scene.background;
		scene.environment.mapping = THREE.EquirectangularReflectionMapping;
		scene.environmentRotation.y = scene.backgroundRotation.y;

	}

	break;

[ycw]

ok, removed the highlight part