Adjust webpack configuration to reflect changes from Gutenberg

* Add the @wordpress/preferences package
* Rename GUTENBERG_PHASE1 to IS_GUTENBERG_PLUGIN
* Remove COMPONENT_SYSTEM_PHASE

package.json

@@ -114,6 +114,7 @@
 		"@wordpress/notices": "3.6.0",
 		"@wordpress/nux": "5.4.0",
 		"@wordpress/plugins": "4.4.0",
+		"@wordpress/preferences": "1.2.0",
 		"@wordpress/primitives": "3.4.0",
 		"@wordpress/priority-queue": "2.6.0",
 		"@wordpress/redux-routine": "4.6.0",

tools/webpack/packages.js

@@ -149,10 +149,8 @@ module.exports = function( env = { environment: 'production', watch: false, buil
 		},
 		plugins: [
 			new DefinePlugin( {
-				// Inject the `GUTENBERG_PHASE` global, used for feature flagging.
-				'process.env.GUTENBERG_PHASE': 1,
-				// Inject the `COMPONENT_SYSTEM_PHASE` global, used for controlling Component System roll-out.
-				'process.env.COMPONENT_SYSTEM_PHASE': 0,
+				// Inject the `IS_GUTENBERG_PLUGIN` global, used for feature flagging.
+				'process.env.IS_GUTENBERG_PLUGIN': 1,
 				'process.env.FORCE_REDUCED_MOTION': JSON.stringify(
 					process.env.FORCE_REDUCED_MOTION
 				),