Make navigation block submenus usable on mobile.

[tellthemachines]

Description

Navigation submenus are currently broken on mobile:

• Their layout assumes a large screen and causes a horizontal scroll on phones;
• On the front end, it's nearly impossible to open a submenu without clicking through to the parent menu link.

This PR adjusts submenu size and placement for small screens, and introduces text wrapping, to avoid horizontal scrolling. It also places the submenu indicator icon outside the menu item link, so that it is possible to open it on a touchscreen without activating the link.

How has this been tested?

Tested on multiple browsers and mobile simulators.

Screenshots

Types of changes

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: -506 B (0%)

Total Size: 889 kB

Filename	Size	Change
build/block-library/index.js	110 kB	-2 B (0%)
build/block-library/style-rtl.css	7.27 kB	-263 B (3%)
build/block-library/style.css	7.28 kB	-269 B (3%)
build/block-library/theme-rtl.css	683 B	+14 B (2%)
build/block-library/theme.css	685 B	+14 B (2%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.02 kB	0 B
build/annotations/index.js	3.4 kB	0 B
build/api-fetch/index.js	3.79 kB	0 B
build/autop/index.js	2.58 kB	0 B
build/blob/index.js	620 B	0 B
build/block-directory/index.js	6.03 kB	0 B
build/block-directory/style-rtl.css	760 B	0 B
build/block-directory/style.css	760 B	0 B
build/block-editor/index.js	102 kB	0 B
build/block-editor/style-rtl.css	10.2 kB	0 B
build/block-editor/style.css	10.2 kB	0 B
build/block-library/editor-rtl.css	7.22 kB	0 B
build/block-library/editor.css	7.22 kB	0 B
build/block-serialization-default-parser/index.js	1.65 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/blocks/index.js	57.5 kB	0 B
build/components/index.js	195 kB	0 B
build/components/style-rtl.css	16.6 kB	0 B
build/components/style.css	16.5 kB	0 B
build/compose/index.js	6.21 kB	0 B
build/core-data/index.js	10.7 kB	0 B
build/data-controls/index.js	1.04 kB	0 B
build/data/index.js	8.23 kB	0 B
build/date/index.js	5.36 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	569 B	0 B
build/dom/index.js	3.05 kB	0 B
build/edit-navigation/index.js	2.75 kB	0 B
build/edit-navigation/style-rtl.css	279 B	0 B
build/edit-navigation/style.css	280 B	0 B
build/edit-post/index.js	92.9 kB	0 B
build/edit-post/style-rtl.css	12.3 kB	0 B
build/edit-post/style.css	12.3 kB	0 B
build/edit-site/index.js	10.1 kB	0 B
build/edit-site/style-rtl.css	5.02 kB	0 B
build/edit-site/style.css	5.02 kB	0 B
build/edit-widgets/index.js	7.17 kB	0 B
build/edit-widgets/style-rtl.css	3.74 kB	0 B
build/edit-widgets/style.css	3.73 kB	0 B
build/editor/editor-styles-rtl.css	399 B	0 B
build/editor/editor-styles.css	400 B	0 B
build/editor/index.js	42.8 kB	0 B
build/editor/style-rtl.css	3.49 kB	0 B
build/editor/style.css	3.49 kB	0 B
build/element/index.js	4.44 kB	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/index.js	6.95 kB	0 B
build/format-library/style-rtl.css	502 B	0 B
build/format-library/style.css	502 B	0 B
build/hooks/index.js	1.93 kB	0 B
build/html-entities/index.js	622 B	0 B
build/i18n/index.js	3.57 kB	0 B
build/is-shallow-equal/index.js	710 B	0 B
build/keyboard-shortcuts/index.js	2.3 kB	0 B
build/keycodes/index.js	1.7 kB	0 B
build/list-reusable-blocks/index.js	2.99 kB	0 B
build/list-reusable-blocks/style-rtl.css	226 B	0 B
build/list-reusable-blocks/style.css	226 B	0 B
build/media-utils/index.js	4.84 kB	0 B
build/notices/index.js	1.57 kB	0 B
build/nux/index.js	3.01 kB	0 B
build/nux/style-rtl.css	616 B	0 B
build/nux/style.css	613 B	0 B
build/plugins/index.js	2.54 kB	0 B
build/primitives/index.js	1.5 kB	0 B
build/priority-queue/index.js	789 B	0 B
build/redux-routine/index.js	2.84 kB	0 B
build/rich-text/index.js	14.5 kB	0 B
build/server-side-render/index.js	2.54 kB	0 B
build/shortcode/index.js	1.69 kB	0 B
build/token-list/index.js	1.28 kB	0 B
build/url/index.js	4.01 kB	0 B
build/viewport/index.js	1.6 kB	0 B
build/warning/index.js	1.14 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

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[karmatosed]

Thanks for this, I think it's a great iteration. I think there probably are even more things we can do to soothe with this, but let's start here. Removing the design feedback label as for now works.