chore: Remove redundant JS in index.html when no feature flags are enabled

[Codex]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

---

This section details on the original issue you should resolve

<issue_title>Redundant JS in index.html when no feature flags are enabled</issue_title>
<issue_description>### Description of the bug

Even if no feature flags are enabled, there's still some related JavaScript in the production index HTML document that doesn't really seem to serve any purpose:

window.Vaadin = window.Vaadin || {};
window.Vaadin.featureFlagsUpdaters = window.Vaadin.featureFlagsUpdaters || [];
window.Vaadin.featureFlagsUpdaters.push((activator) => {
});

Expected behavior

Expected to not have anything about features flags in the HTML if no feature flags are enabled.

Minimal reproducible example

1. Run your favorite app without feature flags enabled in production mode
2. Check the index HTML payload

Versions

• Vaadin / Flow version: 25.1.3</issue_description>

Comments on the Issue (you are @codex[agent] in this section)

[cla-assistant]

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[mshabarov]

1. The failing test

WebComponentProviderTest.webComponentGenerator_responseGetsResult:212 Response should have Feature Flags updater function ==> expected: but was:

should expect no feature flag codes if feature flags are not enabled.

2. Format the code with "mvn spotless:apply".

[Codex]

1. The failing test

WebComponentProviderTest.webComponentGenerator_responseGetsResult:212 Response should have Feature Flags updater function ==> expected: but was:

...

Updated WebComponentProviderTest.webComponentGenerator_responseGetsResult to expect no feature-flag updater when no flags are enabled. Commit: c881ae3

[mshabarov]

@codex[agent] run mvn spotless:apply and commit.

[Codex]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• maven.vaadin.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.14/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.14/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.14 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.14/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/flow/flow org.codehaus.plexus.classworlds.launcher.Launcher -q spotless:apply (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.14/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.14/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.14 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.14/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/flow/flow org.codehaus.plexus.classworlds.launcher.Launcher -q -pl flow-server -am spotless:apply -DspotlessFiles=flow-server/src/main/java/com/vaadin/flow/server/communication/IndexHtmlRequestHandler.java,flow-server/src/test/java/com/vaadin/flow/server/communication/IndexHtmlRequestHandlerTest.java,flow-server/src/test/java/com/vaadin/flow/server/co ndor/bin/git (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.14/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.14/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.14 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.14/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/flow/flow org.codehaus.plexus.classworlds.launcher.Launcher -q -pl flow-server spotless:apply (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

 1 394 files  ±0   1 394 suites  ±0   1h 12m 35s ⏱️ - 2m 49s
10 065 tests ±0   9 995 ✅ ±0  70 💤 ±0  0 ❌ ±0 
10 540 runs  ±0  10 461 ✅ ±0  79 💤 ±0  0 ❌ ±0 

Results for commit d41000d. ± Comparison against base commit 53fedf9.

[mshabarov]

Needs someone's else review.

[caalador]

Missing test that validates that the feature flag code is added if there is a feature in use.

[caalador]

Test name is now wrong as the expectation is that the setter is notPresent.