Sharing: show legacy settings on block themes so users can disable sharing

[shsajalchowdhury]

What

Fixes #49495

Why

When a block-based theme is active on a self-hosted Jetpack site, the Sharing settings page (Settings > Sharing) replaces the full services configuration UI with only a Site Editor prompt. This hides all controls for managing legacy sharing buttons, making it impossible for users to disable the sharing buttons that are automatically appended to post content via the_content filter.

Users have to switch back to a classic theme, disable sharing, then switch back to their block theme — which is a poor UX.

How

Instead of replacing services_config_display() with sharing_block_display(), show both:

1. The block theme message/prompt (encouraging use of the Sharing block)
2. The full legacy services config (so users can manage/disable existing sharing buttons)

Testing Instructions

1. Activate a block-based theme (e.g., Twenty Twenty-Four)
2. Enable Jetpack Sharing module
3. Go to Settings > Sharing
4. Before: Only see a "Go to the site editor" prompt with no way to disable legacy sharing buttons
5. After: See the block theme prompt AND the full services configuration below it, including the ability to remove sharing services and disable content-appended buttons
6. Disable all sharing services and verify buttons no longer appear on posts

Changelog

Sharing: ensure legacy sharing settings remain accessible on block themes so users can disable sharing buttons appended to content.

Does this pull request change what data or activity we track or use?

No. This change only modifies what UI is shown on the Sharing settings page — no data collection or tracking changes.

Testing instructions

1. Activate a block-based theme (e.g., Twenty Twenty-Four)
2. Enable the Jetpack Sharing module
3. Go to Settings > Sharing
4. Before: Only a "Go to the site editor" prompt is shown with no way to disable legacy sharing buttons
5. After: The block theme prompt appears AND the full services configuration is displayed below it — you can remove sharing services and disable content-appended buttons
6. Disable all sharing services and verify that buttons no longer appear on posts

[github-actions]

Thank you for your PR!

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[jeherve]

Could you create the changelog entry again? This is incorrect.

Error: Type must be "major", "enhancement", "compat", "bugfix", or "other".

I would recommend using the built-in CLI tool to generate those entries, to avoid such issues.

Suggested change

	Type: fixed
	Type: bugfix