### What?
- Updates the `RenderTitle` component to check that the `title` is a
string before returning it.
- Adds note to docs that **Relationship** and **Join** fields cannot be
assigned to `useAsTitle`, a **virtual** field should be used instead.
### Why?
When autosave is enabled and the `useAsTitle` points to a relationship
field, the autosave process returns an `object` for the title, this gets
passed to the `RenderTitle` component and throws an error which crashes
the UI.
### How?
Safely checks that `title` is a string before rendering it in
`RenderTitle` and updates docs to clarify that Relationship/Joins are
not compatible with `useAsTitle`.
Fixes#12960
8a5cb27463