Navigation Block: Revert all margins on navigation-item in editor - #37587

Description

This PR reverts the top and bottom margins for each navigation-item in the editor.

The left and right margins are already being reverted to allow this block to work with classic theme auto margins. However, in a theme that doesn't support theme.json, when a background is applied to the navigation block, the default vertical margins from the 'Edit Post' classic stylesheet create too much spacing in the editor, compared to what is output on the front end.

These are the styles from the Edit Post classic stylesheet that these changes override:

html :where(.wp-block) {
	margin-top: $default-block-margin;
	margin-bottom: $default-block-margin;

How has this been tested?

This bug was originally found when working on an issue in the Seedlet theme: Automattic/themes#3684

It can also be tested by activating any other theme that does not support theme.json, and then:

• Insert a navigation block
• Add at least one navigation item
• Apply a background color to the navigation block

There should be larger (or different) vertical margins on the navigation block in the editor compared to the front end.

Screenshots

These are from testing with Seedlet.

Without this PR:

Editor	Front end

With this PR:

Editor	Front end

Types of changes

Enhancement / bug fix

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).