ShaderLib: Implemented @forest-ka shadow fix. See #4341.

src/renderers/shaders/ShaderLib.js

@@ -1282,7 +1282,7 @@ THREE.ShaderLib = {
 
 			"	const vec4 bit_shift = vec4( 256.0 * 256.0 * 256.0, 256.0 * 256.0, 256.0, 1.0 );",
 			"	const vec4 bit_mask  = vec4( 0.0, 1.0 / 256.0, 1.0 / 256.0, 1.0 / 256.0 );",
-			"	vec4 res = fract( depth * bit_shift );",
+			"	vec4 res = mod( depth * bit_shift * vec4( 255 ), vec4( 256 ) ) / vec4( 255 );", // "	vec4 res = fract( depth * bit_shift );",
 			"	res -= res.xxyz * bit_mask;",
 			"	return res;",