passing the CLI option "--enable-proposed-api" without extension id isn't flagged as an error

testing #48427:

I was running "code-insiders" with  the "--enable-proposed-api" option without noticing that the option requires an extension ID.

This should be fixed either by
- reporting an error and aborting "code", or by
- interpreting a missing extension ID as the semantics "enable proposed API for any extension"