fix(): allow initializeApp to be used with AOT

[jamesdaniels]

Checklist

• Issue number for this PR: AngularFireModule.initializeApp(...) fails in ng6 prod build #1635
• Docs included?: no
• Test units included?: yes
• In a clean directory, yarn install, yarn test run successfully? yes

Description

Turns out type guards cannot be used in decorators.

We'd like to keep AngularFireModule.initializeApp in step with the Firebase JS SDK's initializeApp, so I had to change the Injection Tokens yet again; fortunately these were not documented to begin with. Dropping FirebaseAppConfigToken and FirebaseAppNameToken in favor of a new FirebaseNameOrConfigToken.

This will allow AngularFireModule.initializeApp to be used with AOT, which we regressed on in RC.8.

[jamesdaniels]

@codediodeio I think this is an alright solution, thoughts?

[codediodeio]

@jamesdaniels That looks to me, best of both worlds. It fixed the error on my end.

[davideast]

LGTM