Change account verification flow to use simple `myUserInfo` to enable logged-in required items.

Pre-Flight checklist

• Did you check to see if this issue already exists?
• This is a single feature request. (Do not put multiple feature requests in one issue)
• This is not a question or discussion. (Use https://lemmy.ml/c/jerboa for that)

Describe The Feature Request Below

Nearly every lemmy API action which requires an account, is currently surrounded by:

account.doIfReadyElseDisplayInfo(
  appState,
  ctx,
  resources,
  snackbarHostState,
  scope,
  myUserInfoViewModel, (previously SiteViewModel)
  accountViewModel,
) {

• This account verification does a lot of altering and refetching of both the accountViewModel, and the Site/MyUserInfoViewModel, which is dangerous for screens which should not be changing accounts or resetting account info.
• Its cumbersome because now every screen requires many viewModels, which they should really only be reading.

Some recommendations:

• These checks should not really be done just to display or not display buttons, but should only be run on startup or account change.
• Buttons should use myUserInfo != null to determine whether to enable or disable buttons, or hide them entirely. This simple check is how lemmy-ui handles all login-related items.
• The AccountViewModel should probably take in the myUserInfoViewModel and siteViewModels as props, so that it can set them directly when switching accounts, rather than those viewmodels each using flows to watch the accountViewModel.
• It might be necessary to create a dedicated Logging In / Verifying screen, so that when switching accounts from the sidebar, the current screen doesn't need to take in and alter all these viewModels.

Start by tracing account.doIfReadyElseDisplayInfo and the interactions among AccountViewModel, myUserInfoViewModel, and SiteViewModel/siteViewModels. Review how startup and account changes currently trigger verification and refetching. Done means logged-in actions can use myUserInfo for their state without each screen altering or resetting account-related view models.