fix(auth): emit local stored session as the initial session

[grdsdev]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

1. Customer reads the currentSession variable which returns the stored session, without validating if it is expired or not, and lets users in.
2. Then the customer attaches an authStateChange listener and receives initialSession = nil, since the stored session couldn't be refreshed.
3. The user has been logged in but now has no session, making all API calls fail.

Although the behavior above isn't wrong nor a bug, since it is documented that the currentSession may have been expired, it is a behavior that just brings more confusion to the usage.

What is the new behavior?

Added a new trait EmitLocalSessionAsInitialSession for customers to opt-in to the new behavior since this is a breaking change.

supabase.auth.onAuthStateChanges { event, session in 
    if event == .initialSession {
        if let session {
            if session.isExpired {
                // Session exists but has been expired. It will try to refresh it in the background and emit a `tokenRefresh` or `signOut` event depending on the result.
                // Probably should show a loading indicator until a `tokenRefreshed`/`signOut` event is received.
            } else {
                // Session exists and is valid, can let user in.
            }
        } else {
            // Session does not exist, user needs to sign in
        }
    } else if event == .tokenRefreshed {
        assert(session != nil && session?.isExpired == false)
    } else if event == .signOut {
        assert(session == nil)
    }
}

Additional context

#630
#753

[coveralls]

Pull Request Test Coverage Report for Build 18477966756

Details

• 14 of 14 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 77.582%

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Totals
Change from base Build 18462418370:	0.2%
Covered Lines:	5942
Relevant Lines:	7659

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💛 - Coveralls