Navigation Submenu: Add Border and Spacing support

[dhruvikpatel18]

What?

Add border and spacing block support to the Navigation Submenu block.

Why?

Navigation Submenu block is missing border and spacing support.
Part of #43247
Part of #43243

How?

Adds the border and spacing block support in block.json

Testing Instructions

• Go to Global Styles Settings. ( Under Appearance > Editor > Styles > Edit styles > Blocks )
• Ensure the Navigation Submenu block’s border and spacing are configurable via Global Styles.
• Confirm Global Styles apply correctly in both the Editor and Frontend.
• Open the Page or Template where you want to add the menu.
• Add a Navigation block (the container block for all navigation links and Submenus).
• Within the Navigation block, add Submenu block.
• Verify Border, Radius, and Spacing settings are available for this Submenu block.
• Check that block-specific styles (e.g., borders, spacing) take precedence over Global Styles.
• Ensure borders and spacing display correctly in both the Editor and Frontend.

Screenshots or screencast

Submenu.block.mov

[github-actions]

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