Bug 1725145 - Preparation for the hybrid build env. r=necko-reviewers,firefox-build-system-reviewers,valentin,glandium

Automatically generated path that adds flag `REQUIRES_UNIFIED_BUILD = True` to `moz.build`
when the module governed by the build config file is not buildable outside on the unified environment.

This needs to be done in order to have a hybrid build system that adds the possibility of combing
unified build components with ones that are built outside of the unified eco system.

Differential Revision: https://phabricator.services.mozilla.com/D122345