Navigation Component: Semantically create nested lists

[psealock]

Fixes: #25248

Description

Semantically render nested lists. NavigationMenu accepts both NavigationGroup and NavigationItem (or any combination thereof) and will always render correct HTML structure:

<h2></h2>
<ul>
	<li></li>
	<li></li>
	<li>
		<h3></h3>
		<ul>
			<li></li>
			<li></li>
			<li></li>
		</ul>
	</li>
</ul>

See more on nesting lists here: https://developer.mozilla.org/en-US/docs/Learn/HTML/Introduction_to_HTML/HTML_text_fundamentals#Lists

#25248 hypothesises HTML manipulation may be well suited to automation once a way to analyze Navigation children. I don't think that will be required because these changes ensure a correct structure.

How has this been tested?

1. npm run storybook:dev.
2. Look through the markup of the example to ensure structure is correct.
3. Make sure no visual CSS regressions occurred.

Screenshots

Types of changes

Changes make rendering a ul element unneeded. Technically this is breaking, but Navigation code is unreleased and behind __experimental flag.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• 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.

[github-actions]

Size Change: +3 B (0%)

Total Size: 1.2 MB

Filename	Size	Change
build/components/index.js	202 kB	+3 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.67 kB	0 B
build/api-fetch/index.js	3.41 kB	0 B
build/autop/index.js	2.83 kB	0 B
build/blob/index.js	620 B	0 B
build/block-directory/index.js	8.53 kB	0 B
build/block-directory/style-rtl.css	953 B	0 B
build/block-directory/style.css	952 B	0 B
build/block-editor/index.js	128 kB	0 B
build/block-editor/style-rtl.css	11.1 kB	0 B
build/block-editor/style.css	11.1 kB	0 B
build/block-library/editor-rtl.css	8.68 kB	0 B
build/block-library/editor.css	8.68 kB	0 B
build/block-library/index.js	139 kB	0 B
build/block-library/style-rtl.css	7.6 kB	0 B
build/block-library/style.css	7.59 kB	0 B
build/block-library/theme-rtl.css	754 B	0 B
build/block-library/theme.css	754 B	0 B
build/block-serialization-default-parser/index.js	1.88 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/blocks/index.js	47.8 kB	0 B
build/components/style-rtl.css	15.5 kB	0 B
build/components/style.css	15.5 kB	0 B
build/compose/index.js	9.67 kB	0 B
build/core-data/index.js	12.4 kB	0 B
build/data-controls/index.js	1.29 kB	0 B
build/data/index.js	8.55 kB	0 B
build/date/index.js	31.9 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	568 B	0 B
build/dom/index.js	4.47 kB	0 B
build/edit-navigation/index.js	10.7 kB	0 B
build/edit-navigation/style-rtl.css	868 B	0 B
build/edit-navigation/style.css	871 B	0 B
build/edit-post/index.js	305 kB	0 B
build/edit-post/style-rtl.css	6.25 kB	0 B
build/edit-post/style.css	6.23 kB	0 B
build/edit-site/index.js	19.3 kB	0 B
build/edit-site/style-rtl.css	3.14 kB	0 B
build/edit-site/style.css	3.14 kB	0 B
build/edit-widgets/index.js	12.2 kB	0 B
build/edit-widgets/style-rtl.css	2.55 kB	0 B
build/edit-widgets/style.css	2.55 kB	0 B
build/editor/editor-styles-rtl.css	492 B	0 B
build/editor/editor-styles.css	493 B	0 B
build/editor/index.js	45.6 kB	0 B
build/editor/style-rtl.css	3.81 kB	0 B
build/editor/style.css	3.81 kB	0 B
build/element/index.js	4.65 kB	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/index.js	7.71 kB	0 B
build/format-library/style-rtl.css	547 B	0 B
build/format-library/style.css	548 B	0 B
build/hooks/index.js	2.13 kB	0 B
build/html-entities/index.js	621 B	0 B
build/i18n/index.js	3.56 kB	0 B
build/is-shallow-equal/index.js	710 B	0 B
build/keyboard-shortcuts/index.js	2.52 kB	0 B
build/keycodes/index.js	1.94 kB	0 B
build/list-reusable-blocks/index.js	3.12 kB	0 B
build/list-reusable-blocks/style-rtl.css	476 B	0 B
build/list-reusable-blocks/style.css	476 B	0 B
build/media-utils/index.js	5.32 kB	0 B
build/notices/index.js	1.79 kB	0 B
build/nux/index.js	3.4 kB	0 B
build/nux/style-rtl.css	671 B	0 B
build/nux/style.css	668 B	0 B
build/plugins/index.js	2.56 kB	0 B
build/primitives/index.js	1.41 kB	0 B
build/priority-queue/index.js	789 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/rich-text/index.js	13.9 kB	0 B
build/server-side-render/index.js	2.77 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.27 kB	0 B
build/url/index.js	4.06 kB	0 B
build/viewport/index.js	1.85 kB	0 B
build/warning/index.js	1.14 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

_{compressed-size-action}

[Copons]

It was so simple! ✨

Thanks for taking care of this @psealock