Site Editor: Needs a fallback title when the Site Title is empty.

[t-hamano]

Description

Discovered this while looking at #51852.

The dashboard displays the site URL with the protocol and www removed as a fallback if the site title is empty.

On the other hand, the Site Editor shows nothing.

This is especially problematic if the site title itself is changed to a link, as explored in #51852.

Similar to dashboards, I think we need a fallback title.

Step-by-step reproduction instructions

• Empty title on General Settings page.
• Access the Site Editor.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes