Add margin support to Site Tagline

[stacimc]

Description

Part of #30921
Depends on #31808
Adds the margin block support to the Site Tagline block.

How has this been tested?

Manually.

1. Using a blocks theme such as Twenty Twenty-One Blocks, update the theme.json to enable margin support under the defaults or the core/site-title context:

                "spacing": {
			"customPadding": true,
			"customMargin": true,
			"units": [
				"px",
				"em",
				"rem",
				"vh",
				"vw"
			]
		},

2. Open the site editor, and select the Site Tagline block.
3. Open the Settings sidebar and expand the spacing settings panel in the inspector controls sidebar.
4. Verify that the controls for both Padding and Margin are present.
5. Modify the block's margins and verify that it looks as expected.
6. Save the post and view on the frontend, confirming the Site Tagline displays correctly. This depends on Spacing support: Add server-side support for margins #31808.

Screenshots

Types of changes

New feature (non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[carolinan]

Works well for me.

[apeatling]

👍