Add METALLIC to light() built-ins

(cherry picked from commit 1300fc7307b7a9a29055c60ff381af03f7a050a0)

servers/visual/shader_types.cpp

@@ -145,6 +145,7 @@ ShaderTypes::ShaderTypes() {
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["ATTENUATION"] = constt(ShaderLanguage::TYPE_VEC3);
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["ALBEDO"] = constt(ShaderLanguage::TYPE_VEC3);
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["TRANSMISSION"] = constt(ShaderLanguage::TYPE_VEC3);
+	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["METALLIC"] = constt(ShaderLanguage::TYPE_FLOAT);
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["ROUGHNESS"] = constt(ShaderLanguage::TYPE_FLOAT);
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["DIFFUSE_LIGHT"] = ShaderLanguage::TYPE_VEC3;
 	shader_modes[VS::SHADER_SPATIAL].functions["light"].built_ins["SPECULAR_LIGHT"] = ShaderLanguage::TYPE_VEC3;