plugin: webviews on development host do not work on electron

Bug Description:

On electron, and when starting the development host (plugin-system) webviews fail to properly start due to a service worker error:

Uncaught (in promise) DOMException: Failed to register a ServiceWorker: The document is in an invalid state.

Steps to Reproduce:

1. open https://github.com/microsoft/vscode-extension-samples/tree/main/webview-sample as a workspace
2. build the extension (npm i)
3. start the debug configuration run extension
4. the development host should start
5. trigger the command cat coding: start cat coding session
6. the webview editor opens but there is no content with the above error

Additional Info

• Operating System: Windows 10
• Theia Version: latest