Fix build based on Christina's input

Thanks Christina for the input here. Changes are
- Add  entry in changeset file
- Add eslintrc.js to `messaging-compat`

Author: zwu52

.changeset/config.json

@@ -23,6 +23,7 @@
     "@firebase/installations-exp",
     "@firebase/installations-compat",
     "@firebase/messaging-exp",
+    "@firebase/messaging-compat",
     "@firebase/performance-exp",
     "@firebase/performance-compat",
     "@firebase/remote-config-exp",

packages-exp/messaging-compat/.eslintrc.js

@@ -0,0 +1,28 @@
+/* eslint-disable @typescript-eslint/no-require-imports */
+/**
+ * @license
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+const path = require('path');
+
+module.exports = {
+  extends: '../../config/.eslintrc.js',
+  parserOptions: {
+    project: 'tsconfig.json',
+    // to make vscode-eslint work with monorepo
+    // https://github.com/typescript-eslint/typescript-eslint/issues/251#issuecomment-463943250
+    tsconfigRootDir: __dirname
+  }
+};