Fix titleless post snippets

[pranvinit]

What?

Shows an excerpt or content snippet alongside (no title) for titleless post records in post/page DataViews, parent selectors, and media “Attached to” fields.

Why?

Titleless posts currently appear only as (no title), or sometimes with an ID, which makes them hard to identify. A short excerpt/content snippet gives users a more human-friendly way to distinguish records.

How?

Adds shared post title fallback helpers in @wordpress/fields, updates post/page title fields and parent selectors to use them, and expands parent selector queries to request excerpt/content. Adds matching media-field fallback logic for embedded attached posts.

Testing Instructions

1. Create or edit a post/page with no title and an excerpt or content.
2. Open a posts/pages DataViews list and confirm it shows (no title) followed by the snippet.
3. Open a page parent selector and confirm titleless parent options show the snippet.
4. Attach media to a titleless post/page and confirm the “Attached to” field shows the snippet.

Testing Instructions for Keyboard

1. Use Tab to navigate to the parent selector or media “Attached to” combobox.
2. Open and move through options with the keyboard.
3. Confirm titleless records are identifiable by the (no title) snippet text.

Use of AI Tools

Used ChatGPT/Codex to help implement, test, and draft this PR. All changes were reviewed by the contributor.