Support reusable blocks in widgets editor

[adamziel]

Description

Related to #22875

This adds support for inserting reusable blocks into widgets editor. Support for creating new reusable blocks is not included in this PR.

How has this been tested?

1. Make sure you have some reusable blocks, if you don't then create a few in the post editor
2. Go to the new widgets editor
3. Open inserter
4. Confirm it has "Reusable blocks" tab
5. Confirm the tab contains all your reusable blocks and that you're able to insert them into the editor

Types of changes

New feature (non-breaking change which adds functionality)

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: +84 B (0%)

Total Size: 1.18 MB

Filename	Size	Change
build/block-directory/index.js	8.6 kB	+1 B
build/block-editor/index.js	129 kB	-2 B (0%)
build/block-library/index.js	135 kB	+2 B (0%)
build/blocks/index.js	47.5 kB	-1 B
build/components/index.js	169 kB	-1 B
build/data/index.js	8.6 kB	-3 B (0%)
build/edit-navigation/index.js	10.7 kB	+1 B
build/edit-post/index.js	306 kB	+2 B (0%)
build/edit-site/index.js	20.4 kB	-2 B (0%)
build/edit-widgets/index.js	21.3 kB	+87 B (0%)
build/format-library/index.js	7.49 kB	-1 B
build/redux-routine/index.js	2.85 kB	+1 B

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.52 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/style-rtl.css	943 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-editor/style-rtl.css	10.9 kB	0 B
build/block-editor/style.css	10.9 kB	0 B
build/block-library/editor-rtl.css	8.65 kB	0 B
build/block-library/editor.css	8.65 kB	0 B
build/block-library/style-rtl.css	7.66 kB	0 B
build/block-library/style.css	7.65 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	1.78 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/components/style-rtl.css	15.3 kB	0 B
build/components/style.css	15.3 kB	0 B
build/compose/index.js	9.42 kB	0 B
build/core-data/index.js	12 kB	0 B
build/data-controls/index.js	685 B	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/style-rtl.css	868 B	0 B
build/edit-navigation/style.css	871 B	0 B
build/edit-post/style-rtl.css	6.29 kB	0 B
build/edit-post/style.css	6.27 kB	0 B
build/edit-site/style-rtl.css	3.84 kB	0 B
build/edit-site/style.css	3.84 kB	0 B
build/edit-widgets/style-rtl.css	3 kB	0 B
build/edit-widgets/style.css	3 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	43.2 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	4.44 kB	0 B
build/escape-html/index.js	733 B	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	621 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	2.39 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	1.34 kB	0 B
build/priority-queue/index.js	788 B	0 B
build/reusable-blocks/index.js	4.6 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	1.69 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	1.74 kB	0 B
build/warning/index.js	1.13 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

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[adamziel]

This is outdated, let's create a new one once #25859 lands.