Enable cross origin extension host if extension marketplace is enabled

Issue: Uninstall perviously installed Extensions when ... (#460284 - closed)

Depends on: fix: remove messagePort hack for crossOriginExt... (gitlab-web-ide!313 - merged)

What does this MR do and why?

As discussed in our sync, this MR introduces a failsafe to enable the cross origin extension host flag if the extension marketplace is enabled.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No UI changes, unit tests should suffice

How to set up and validate locally

Follow steps outlined here to setup Extensions Marketplace : !151352 (merged)++