Use ToolbarButtons instead of Buttons in the Legacy Widget block's toolbar

[talldan]

Description

When testing the widget screen I noticed the block toolbar for the Legacy Widget Block doesn't use a Roving Tab Index. The toolbar instead has a tab stop for each button.

This is caused by the block using Button components instead of ToolbarButton components. This PR switches over the component. There's no visual change.

How has this been tested?

1. Navigate to the widgets screen.
2. Add a legacy widget block
3. Shift+Tab to the block toolbar
4. Observe the first item is focused (on master the last item is focused)
5. Use left/right arrow keys to navigate to around the toolbar.
6. Use left/right arrow keys to focus the 'Edit' button
7. Press Tab, observe focus is moved back to the block (on master the preview button is focused)

Types of changes

Bug fix (non-breaking change which fixes an issue)

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: 1.19 MB

Filename	Size	Change
build/edit-widgets/index.js	22.3 kB	+3 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.54 kB	0 B
build/api-fetch/index.js	3.35 kB	0 B
build/autop/index.js	2.72 kB	0 B
build/blob/index.js	668 B	0 B
build/block-directory/index.js	8.61 kB	0 B
build/block-directory/style-rtl.css	943 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-editor/index.js	130 kB	0 B
build/block-editor/style-rtl.css	11 kB	0 B
build/block-editor/style.css	10.9 kB	0 B
build/block-library/editor-rtl.css	8.93 kB	0 B
build/block-library/editor.css	8.93 kB	0 B
build/block-library/index.js	144 kB	0 B
build/block-library/style-rtl.css	7.71 kB	0 B
build/block-library/style.css	7.71 kB	0 B
build/block-library/theme-rtl.css	741 B	0 B
build/block-library/theme.css	741 B	0 B
build/block-serialization-default-parser/index.js	1.77 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/blocks/index.js	47.6 kB	0 B
build/components/index.js	170 kB	0 B
build/components/style-rtl.css	15.4 kB	0 B
build/components/style.css	15.4 kB	0 B
build/compose/index.js	9.63 kB	0 B
build/core-data/index.js	12.1 kB	0 B
build/data-controls/index.js	683 B	0 B
build/data/index.js	8.63 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	569 B	0 B
build/dom/index.js	4.43 kB	0 B
build/edit-navigation/index.js	10.6 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	306 kB	0 B
build/edit-post/style-rtl.css	6.37 kB	0 B
build/edit-post/style.css	6.35 kB	0 B
build/edit-site/index.js	21.6 kB	0 B
build/edit-site/style-rtl.css	3.8 kB	0 B
build/edit-site/style.css	3.81 kB	0 B
build/edit-widgets/style-rtl.css	3.09 kB	0 B
build/edit-widgets/style.css	3.09 kB	0 B
build/editor/editor-styles-rtl.css	480 B	0 B
build/editor/editor-styles.css	482 B	0 B
build/editor/index.js	42.6 kB	0 B
build/editor/style-rtl.css	3.85 kB	0 B
build/editor/style.css	3.84 kB	0 B
build/element/index.js	4.45 kB	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/index.js	7.49 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	1.74 kB	0 B
build/html-entities/index.js	622 B	0 B
build/i18n/index.js	3.54 kB	0 B
build/is-shallow-equal/index.js	709 B	0 B
build/keyboard-shortcuts/index.js	2.38 kB	0 B
build/keycodes/index.js	1.85 kB	0 B
build/list-reusable-blocks/index.js	3.02 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	5.12 kB	0 B
build/notices/index.js	1.69 kB	0 B
build/nux/index.js	3.27 kB	0 B
build/nux/style-rtl.css	671 B	0 B
build/nux/style.css	668 B	0 B
build/plugins/index.js	2.44 kB	0 B
build/primitives/index.js	1.35 kB	0 B
build/priority-queue/index.js	789 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/reusable-blocks/index.js	3.06 kB	0 B
build/rich-text/index.js	13 kB	0 B
build/server-side-render/index.js	2.61 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.24 kB	0 B
build/url/index.js	4.06 kB	0 B
build/viewport/index.js	1.75 kB	0 B
build/warning/index.js	1.13 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

_{compressed-size-action}

[draganescu]

Tested this and works as described