Fix: Proper Detection of ES Modules in Federated Extension Loader

🔧 Problem

The federated extension loader does not reliably detect when an extension is using ES modules.
Even when extensions output valid ESM bundles, the loader defaults to treating them as CommonJS,
which can cause load failures depending on how the extension was built.

✅ What This PR Does

This PR updatesdev_mode/bootstrap.js to improve ES module detection in federated extensions.

Key Improvements

• Detects ESM based on.mjs file extension.
• Checks page-config metadata (federated_extensions) foresModule: true.
• Ensures correct script type is used during dynamic loading.

📁 Files Changed

• dev_mode/bootstrap.js

🧪 Testing

I could not reproduce the module-format error locally, but the logic follows the expected behavior
and aligns with the discussion in the linked issue. Feedback from maintainers on validation
with real-world extension setups is appreciated.

📌 Related Issue

Fixes#17809