Block Navigator: Use default block appender

[noisysocks]

Fixes #22170.

Changes the Block Navigator to use the default block appender instead of the button block appender.

Before	After

To test:

1. Go to Gutenberg → Experiments and enable the Navigation experiment.
2. Go to Navigation.
3. Observe the new appender icons.

[github-actions]

Size Change: -15.3 kB (1%)

Total Size: 1.11 MB

Filename	Size	Change
build/api-fetch/index.js	3.4 kB	-1 B
build/block-directory/index.js	6.48 kB	-452 B (6%)	✅
build/block-directory/style-rtl.css	787 B	-3 B (0%)
build/block-directory/style.css	787 B	-4 B (0%)
build/block-editor/index.js	105 kB	+245 B (0%)
build/block-editor/style-rtl.css	11.3 kB	+431 B (3%)
build/block-editor/style.css	11.3 kB	+433 B (3%)
build/block-library/editor-rtl.css	7.61 kB	+440 B (5%)	🔍
build/block-library/editor.css	7.61 kB	+441 B (5%)	🔍
build/block-library/index.js	119 kB	+20 B (0%)
build/block-library/style-rtl.css	7.68 kB	+198 B (2%)
build/block-library/style.css	7.68 kB	+199 B (2%)
build/block-serialization-default-parser/index.js	1.88 kB	-1 B
build/components/index.js	190 kB	-4 B (0%)
build/components/style-rtl.css	19.5 kB	+2.39 kB (12%)	⚠️
build/components/style.css	19.5 kB	+2.4 kB (12%)	⚠️
build/compose/index.js	9.32 kB	+36 B (0%)
build/core-data/index.js	11.4 kB	+13 B (0%)
build/data-controls/index.js	1.29 kB	-3 B (0%)
build/data/index.js	8.43 kB	+4 B (0%)
build/date/index.js	5.47 kB	-2 B (0%)
build/edit-navigation/index.js	7.88 kB	+1.25 kB (15%)	⚠️
build/edit-post/index.js	302 kB	+48 B (0%)
build/edit-post/style-rtl.css	5.43 kB	-6.79 kB (125%)	🏆
build/edit-post/style.css	5.43 kB	-6.79 kB (125%)	🏆
build/edit-site/index.js	14.1 kB	+275 B (1%)
build/edit-site/style-rtl.css	2.96 kB	-2.57 kB (87%)	🏆
build/edit-site/style.css	2.96 kB	-2.58 kB (87%)	🏆
build/edit-widgets/index.js	8.88 kB	+1.01 kB (11%)	⚠️
build/edit-widgets/style-rtl.css	2.4 kB	-2.17 kB (90%)	🏆
build/edit-widgets/style.css	2.4 kB	-2.17 kB (90%)	🏆
build/editor/index.js	44.6 kB	+4 B (0%)
build/editor/style-rtl.css	4.26 kB	-793 B (18%)	👏
build/editor/style.css	4.27 kB	-793 B (18%)	👏
build/element/index.js	4.64 kB	-2 B (0%)
build/format-library/index.js	7.71 kB	+4 B (0%)
build/hooks/index.js	2.13 kB	+1 B
build/keyboard-shortcuts/index.js	2.51 kB	+3 B (0%)
build/list-reusable-blocks/index.js	3.12 kB	-3 B (0%)
build/notices/index.js	1.79 kB	+1 B
build/nux/index.js	3.4 kB	+3 B (0%)
build/plugins/index.js	2.56 kB	-1 B
build/rich-text/index.js	14.8 kB	-2 B (0%)
build/server-side-render/index.js	2.68 kB	+1 B
build/viewport/index.js	1.84 kB	-2 B (0%)
build/wordcount/index.js	1.17 kB	-2 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.62 kB	0 B
build/autop/index.js	2.83 kB	0 B
build/blob/index.js	620 B	0 B
build/block-library/theme-rtl.css	684 B	0 B
build/block-library/theme.css	686 B	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/blocks/index.js	48.1 kB	0 B
build/deprecated/index.js	771 B	0 B
build/dom-ready/index.js	568 B	0 B
build/dom/index.js	3.11 kB	0 B
build/edit-navigation/style-rtl.css	857 B	0 B
build/edit-navigation/style.css	856 B	0 B
build/editor/editor-styles-rtl.css	425 B	0 B
build/editor/editor-styles.css	428 B	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/style-rtl.css	502 B	0 B
build/format-library/style.css	502 B	0 B
build/html-entities/index.js	622 B	0 B
build/i18n/index.js	3.56 kB	0 B
build/is-shallow-equal/index.js	711 B	0 B
build/keycodes/index.js	1.94 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	5.29 kB	0 B
build/nux/style-rtl.css	616 B	0 B
build/nux/style.css	613 B	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	2.85 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.28 kB	0 B
build/url/index.js	4.02 kB	0 B
build/warning/index.js	1.14 kB	0 B

_{compressed-size-action}

[draganescu]

This LGTM 🚀

[mtias]

Thanks!