[Auth] Forward secure coding calls for TOTPMultiFactorInfo

[ncooke3]

Fix #13591

• Remove unneeded totpInfo property because it's not used. The property on AuthProtoMFAEnrollment is enough (e.g. git grep "\.totpInfo" -- FirebaseAuth/Sources/Swift.

  firebase-ios-sdk/FirebaseAuth/Sources/Swift/Backend/RPC/Proto/AuthProtoMFAEnrollment.swift

  Line 19 in ed4269b

  let totpInfo: NSObject?

---

nickcooke@nickcooke-mac firebase-3 % git grep "\.totpInfo" -- FirebaseAuth/Sources/Swift
FirebaseAuth/Sources/Swift/Backend/AuthBackend.swift:          } else if let _ = enrollment.totpInfo {
FirebaseAuth/Sources/Swift/MultiFactor/MultiFactor.swift:        } else if enrollment.totpInfo != nil {

[ncooke3]

Despite being marked unavailable, this class's init?(coder:) is actually called when totp is registered:

firebase-ios-sdk/FirebaseAuth/Sources/Swift/MultiFactor/MultiFactor.swift

Line 289 in 60b6dd5

coder.encode(enrolledFactors, forKey: kEnrolledFactorsCodingKey)

[paulb777]

Thanks!

Will need to be cherry-picked to 11.2 branch as well.

[ncooke3]

I'm not sure now is the time to address it, but TOTPMultiFactorInfo is not public but PhoneMultiFactorInfo is. This also applies to 10.29.0.

[ncooke3]

Typing this with a more specific type (dictionary) added a more code to cast it during encoding and decoding. I stepped back and see that this property is never read from (it's only read from from the AuthProtoMFAEnrollment.swift class). I think it's better to just remove it as it's addition is more confusing.

[ncooke3]

I was able to successfully enroll via TOTP in the sample app using these changes.