Fix bug which caused app not to load correctly when force_verification is enabled

[richvdh]

Review commit-by-commit, but in short, this is a fix for #31203.

In slightly longer terms: #31203 was happening due to a condition added in onShowPostLoginScreen in #29487, to avoid the following situation:

• onLoggedIn calls onShowPostLoginScreen
• which (without the check) would call showScreenAfterLogin
• which would queue up an action Action.ViewHomePage
• Then we would receive an already-queued ClientStarted action, which would transition us (correctly) to the COMPLETE_SECURITY view
• Then we would receive the ViewHomePage action, taking us back to LOGGED_IN.

I don't think the check was necessary in practice, because in practice there would be enough delay between the OnLoggedIn and ClientStarted actions that the race didn't happen.

The problem with the check was that it meant that, whenever force_verification was enabled, we would get stuck in the LOADING state.

This PR solves the race a different way (by adding an intermediate state that happens in onLoggedIn, and waiting for the client to start before calling onShowPostLoginScreen); that means we can get rid of the condition on shouldForceVerification and hence fix the bug.

Fixes: #31203