What?

Adds support for a custom title placeholder in the Post Title block, driven by the post type's supports data. This lets post types define their own placeholder text (e.g., "Add product name" instead of the generic "Title").

Closes #75938

How?

• Reads the title support data from the post type via getPostType() — when it's an array, the first element can include a placeholder property
• Uses that placeholder throughout the block: in the static preview, the editable input, and the linked title variants
• Splits the non-editable rendering into separate branches to avoid passing placeholder text through dangerouslySetInnerHTML
• The "(no title)" fallback remains untouched.
• Fully backwards compatible.

Testing Instructions

1. Register a custom post type with title support that includes a placeholder (e.g., 'supports' => array( 'title' => array( 'placeholder' => 'Product name' ), 'editor' ))
2. Add a Post Title block in a template or Query Loop targeting that post type
3. Notice the placeholder displays your custom text instead of "Title""
4. Verify standard post types (post, page) still show the default "Title" text

Screenshots

Example via tweaking WooCommerce product CPT: