build: mark layout package as sideEffect-free for webpack v4 (#709)

Author: CaerusKaru

src/lib/package.json

@@ -30,5 +30,6 @@
   },
   "dependencies": {
     "tslib": "^1.7.1"
-  }
+  },
+  "sideEffects": false
 }

tools/package-tools/entry-point-package-json.ts

@@ -10,6 +10,7 @@ export function createEntryPointPackageJson(destDir: string, packageName: string
     main: `../bundles/${packageName}-${entryPointName}.umd.js`,
     module: `../esm5/${entryPointName}.es5.js`,
     es2015: `../esm2015/${entryPointName}.js`,
+    sideEffects: false,
   };
 
   writeFileSync(join(destDir, 'package.json'), JSON.stringify(content, null, 2), 'utf-8');