This PR makes sure that the file and native realms are always added to the
beginning of the realm chain unless explicitly disabled.
Currently, they are only impliciltly added when:
* No other realms are configured
* No configured realms can be used with current license (so an expired license
can fallback to these basic realms)
A side effect (intended?) is that file and native realm cannot be truely
disabled at all time because the above two rules always apply regardless
whether the realms are disabled or not.
This PR makes the behaviour more explicit. If the file or native realm is
explicitly disabled, it will be disabled at all time. If they are not
explicitly disabled, they will always be added to the beginning of the realm
chain. Two scenarios are possible:
* File or native realm is explicitly configured. In this case, their order
value must be provided and honoured
* File or native realm is not configured. In this case, they are implicitly
added to the beginning of the realm chain (file then native).
The order config must be explicitly specified for each realm.
It must also be unique for each realm.
This is a breaking change and will begin to take effect in 8.0
Resolves: #37614
Yang Wang
Lisa Cawley