### What?
Prevents the Auth component from rendering an empty `.auth-fields`
wrapper.
### Why?
When `disableLocalStrategy` is true and `enableFields` is false, but
`useAPIKey` is true while
read access to API key fields is denied, the component still rendered
the parent wrapper with a
background—showing a blank box.
### How?
Introduce `hasVisibleContent`:
- `showAuthBlock = enableFields`
- `showAPIKeyBlock = useAPIKey && canReadApiKey`
- `showVerifyBlock = verify && isEditing`
If none are true, return `null`. (`disableLocalStrategy` is already
accounted for via `enableFields`.)
Fixes#12089
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810184269d