Donations Form Block: Attach the Donations pattern

### Impacted plugin

Jetpack

### What

Give users a direct way to convert the block into the pattern

### How

This is a follow up to https://github.com/Automattic/wp-calypso/issues/61907

Attach the Donations pattern to the Donations Form block with the [contextual pattern transformation](https://developer.wordpress.org/block-editor/reference-guides/block-api/block-patterns/#block-patterns-contextual-to-block-types-and-pattern-transformations) functionality.

Start by locating the Donations Form block and Donations pattern definitions, then read the linked contextual pattern transformation documentation and the follow-up issue. Done means the block exposes the Donations pattern as a direct transformation and the transformation works in the editor.

Written by the indexing model from the issue text.