Add Storage emulator snippets that were previously hard-coded in docs. (#304)

* Initial push to prepare for review.

* Fix lint error.

* Generate /snippets/storage-next/emulator-suite.

* Fix errant RTDB reference in comment lines.

Author: markarndt

snippets/storage-next/emulator-suite/storage_emulator_connect.js

@@ -0,0 +1,15 @@
+// This snippet file was generated by processing the source file:
+// ./storage-next/emulator-suite.js
+//
+// To update the snippets in this file, edit the source and then run
+// 'npm run snippets'.
+
+// [START storage_emulator_connect_modular]
+import { getStorage, connectStorageEmulator } from "firebase/storage";
+
+const storage = getStorage();
+if (location.hostname === "localhost") {
+  // Point to the Storage emulator running on localhost.
+  connectStorageEmulator(storage, "localhost", 9199);
+} 
+// [END storage_emulator_connect_modular]

storage-next/emulator-suite.js

@@ -0,0 +1,14 @@
+// [SNIPPET_REGISTRY disabled]
+// [SNIPPETS_SEPARATION enabled]
+
+function onDocumentReady() {
+  // [START storage_emulator_connect]
+  const { getStorage, connectStorageEmulator } = require("firebase/storage");
+
+  const storage = getStorage();
+  if (location.hostname === "localhost") {
+    // Point to the Storage emulator running on localhost.
+    connectStorageEmulator(storage, "localhost", 9199);
+  } 
+  // [END storage_emulator_connect]
+}

storage/emulator-suite.js

@@ -0,0 +1,16 @@
+// These samples are intended for Web so this import would normally be
+// done in HTML however using modules here is more convenient for
+// ensuring sample correctness offline.
+import firebase from "firebase/app";
+import "firebase/storage";
+
+function onDocumentReady() {
+  // [START storage_emulator_connect]
+  var storage = firebase.storage();
+  if (location.hostname === "localhost") {
+    // Point to the Storage emulator running on localhost.
+    storage.useEmulator("localhost", 9199);
+  } 
+  // [END storage_emulator_connect]
+}
+