Enhancement: Sharing Buttons block: Add support for share counts and official button styles

### Impacted plugin

Jetpack

### What

The [Sharing Buttons block](https://jetpack.com/support/sharing/) currently lacks support for two key features that are available in the classic Jetpack sharing buttons:

- Displaying share counts (e.g., number of Facebook shares).
- Using official button styles (e.g., branded color and design from platforms like Facebook).

Users who switch to block themes or rely on the block-based UI lose these capabilities.

### How

- Add an option to enable share counts in the Sharing Buttons block
- Add a toggle or style selection for “official” button styles (to match the native design of platforms like Facebook, LinkedIn, X, etc.)

This would bring feature parity between the classic Jetpack sharing buttons and the block-based version.

The issue names the Sharing Buttons block and the classic Jetpack sharing buttons; start by locating both implementations and comparing their existing share-count and official-style behavior. Done means the block exposes both requested options and provides feature parity for the listed sharing services.

Written by the indexing model from the issue text.