Use <number>.<number> format for Google Analytics client ID

With the `ENFORCE_RECOMMENDATIONS` [validation behavior](https://developers.google.com/analytics/devguides/collection/protocol/ga4/validating-events?client_type=firebase#send_events_for_validation), Google Analytics warns about client IDs not in the <number>.<number> format.

This is not an issue in practice - that recommendation is for compatibility with existing client IDs and events are still processed with a client ID in any format. Additionally, the validation is not enabled by default.

However, this PR updates our sample code to use a consistent ID regardless to reduce noise if the validation is enabled. We use a random ID concatenated with a UNIX timestamp to match other GA client libraries.

Author: oliverdunk

functional-samples/tutorial.google-analytics/scripts/google-analytics.js

@@ -14,14 +14,27 @@ class Analytics {
     this.debug = debug;
   }
 
+  getRandomId() {
+    const digits = "123456789".split("");
+    let result = "";
+
+    for (let i = 0; i < 10; i++) {
+      result += digits[Math.floor(Math.random() * 9)]
+    }
+
+    return result;
+  }
+
   // Returns the client id, or creates a new one if one doesn't exist.
   // Stores client id in local storage to keep the same client id as long as
   // the extension is installed.
   async getOrCreateClientId() {
     let { clientId } = await chrome.storage.local.get('clientId');
     if (!clientId) {
-      // Generate a unique client ID, the actual value is not relevant
-      clientId = self.crypto.randomUUID();
+      // Generate a unique client ID, the actual value is not relevant. We use
+      // the <number>.<number> format since this is typical for GA client IDs.
+      const unixTimestampSeconds = Math.floor(new Date().getTime() / 1000);
+      clientId = `${this.getRandomId()}.${unixTimestampSeconds}`;
       await chrome.storage.local.set({ clientId });
     }
     return clientId;