Site Logo: Add setting labels via the 'register_setting' method

[Mamaduka]

What?

PR updates the Site Logo block to provide setting labels via the registration function instead of using the shim.

Why?

Unlike other core settings, these are associated with the block and must be synced via package updates. I remembered this while working on WordPress/wordpress-develop#6495.

Testing Instructions

1. Open a post.
2. Add a Site Logo block.
3. Select an image.
4. Save the post.
5. Confirm setting labels are correctly displayed.

Testing Instructions for Keyboard

Same.

Screenshots or screencast

[github-actions]

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Co-authored-by: Mamaduka <[email protected]>
Co-authored-by: t-hamano <[email protected]>

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[t-hamano]

LGTM 👍

[Mamaduka]

Thanks for testing, @t-hamano!