Centralise calls to `emberSafeRequire`

[BlueCutOfficial]

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• ❌ GlimmerRuntime
• ❌ GlimmerReference
• ✅ GlimmerManager
• ✅ GlimmerUtil
• ✅ EmberDestroyable

I isolated the changes to identify better which caused the tests to fail. The current 4 fails are caused by GlimmerRuntime (and if I changed only GlimmerReference then I have different set of 6 fails that doesn't appear for now). The other changes doesn't cause 3.24 scenario to fail.

After debugging the 3.24 app with Chris, we found out the root cause of the issue is the circular dependency between the util/ember and the util/ember/loader. It causes the Ember used in util/ember/loader to be undefined instead of being already assigned to the Ember defined in util/ember. Fixing the circular dependency has side effects that must be handled so we will open a dedicated PR before coming back to this one.

Description

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