Add ident to loaders passed to child compilation

add test case how css deduplication works

src/loader.js

@@ -51,6 +51,7 @@ export function pitch(request) {
           return ({
             loader: loader.path,
             options: loader.options,
+            ident: loader.ident,
           });
         });
       }

test/cases/composes-async/async-1.css

@@ -0,0 +1,4 @@
+:local .base {
+  composes: composed from './async-2.css';
+  background: blue;
+}

test/cases/composes-async/async-2.css

@@ -0,0 +1,3 @@
+:local .composed {
+  background: green;
+}

test/cases/composes-async/expected/1.css

@@ -0,0 +1,4 @@
+.base {
+  background: blue;
+}
+

test/cases/composes-async/expected/3.css

@@ -0,0 +1,4 @@
+.composed {
+  background: green;
+}
+

test/cases/composes-async/index.js

@@ -0,0 +1,2 @@
+import('./async-1.css');
+import('./async-2.css');

test/cases/composes-async/webpack.config.js

@@ -0,0 +1,38 @@
+const Self = require('../../../');
+
+module.exports = {
+  entry: './index.js',
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          Self.loader,
+          {
+            loader: 'css-loader',
+            options: {
+              localIdentName: '[local]'
+            }
+          }
+        ],
+      },
+    ],
+  },
+  optimization: {
+    splitChunks: {
+      cacheGroups: {
+        cssDedupe: {
+          test: /\.css$/,
+          chunks: 'all',
+          minChunks: 2,
+          enforce: true
+        }
+      }
+    }
+  },
+  plugins: [
+    new Self({
+      filename: '[name].css',
+    }),
+  ],
+};