fix(schematics): rewrite `projectFromRc` and add spec file

[nontangent]

Checklist

• [x] Issue number for this PR: https://github.com/angular/angularfire/issues/3077 (required)
• [x] Docs included?: no
• [x] Test units included?: yes
• [x] In a clean directory, yarn install, yarn test run successfully? (yes/no; required)

Description

Fix https://github.com/angular/angularfire/issues/3077 and add unit tests.

Code sample

No API changes.

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[arlopezg]

I think this would fix https://github.com/angular/angularfire/issues/3309