PHP-only blocks: in-canvas editing

[priethor]

WordPress 7.0 introduced PHP-only block registration through supports.autoRegister. These blocks currently use a render_callback, so the editor displays a server-rendered preview rather than editable blocks, and can't be editable in-canvas.

This ticket tracks the WordPress Core changes for the in-canvas editing of PHP-only blocks, in particular the pattern-based approach explored in ​Gutenberg PR #80182:

• It lets a PHP-only block provide a pattern instead of a render callback, so its content can be edited directly in the canvas.
• Patterns stay synced by default, and block authors choose which fields can be edited on each instance through pattern overrides.
• A PHP-only block can provide either a render_callback or a pattern. If both are registered, WordPress reports incorrect usage and uses the pattern.