`FIRMultiFactor` does not support `NSSecureCoding` correctly

[igor-makarov]

Description

The FIRMultiFactor conforms to NSSecureCoding but does not support it correctly.

According to Apple:

An object that does override init(coder:) must decode any enclosed objects using the decodeObjectOfClass:forKey: method.

(NSSecureCoding documentation)

In addition, the user property is a weak reference to parent object and should be set outside encode/decode.

Reproducing the issue

No response

Firebase SDK Version

10.3.0

Xcode Version

14.1

Installation Method

CocoaPods

Firebase Product(s)

Authentication

Targeted Platforms

iOS

Relevant Log Output

No response

If using Swift Package Manager, the project's Package.resolved

No response

If using CocoaPods, the project's Podfile.lock

No response

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[igor-makarov]

@paulb777 I've encountered this and already have a fix in #10633.