Improve magic link flow to avoid a flash of "requesting magic link" screen

[rachelmcr]

As discussed in woocommerce/woocommerce-android#3268 (comment), the current magic link login flow shows a flash of the "requesting magic link" screen, but users no longer need to manually request that link. Instead, we proceed automatically to the "magic link sent" screen like this:

We should improve that experience. @AmandaRiu explained:

That screen you see flashing is just the "requesting magic link" screen which you'll want to show if someone has a slow connection (otherwise it will feel like the app has frozen). We could and should change the designs around this but I think in that case it'd make sense to coordinate with WPAndroid as well since these screens are part of the shared flow the two apps use. If the designs could join the "Requesting magic link" and "magic link sent" into a single view where maybe there's a progress animation then the flow wouldn't feel so jarring.