Fix Legacy Widgets: Widgets with special chars on classname did not load

[jorgefilipecosta]

Widgets with special chars on their class name did not loaded on legacy widgets.
For example, there are widgets whose classname is "WPCW\Contact".
This PR address this issue.

How has this been tested?

I installed https://wordpress.org/plugins/contact-widgets/.
I verified I can select the "Contact Details" widget on the legacy widgets block and its form loads on the dom (on master nothing loads). It is still not possible to drag and drop form fields around but that is a separate JS issue.

[github-actions]

Size Change: +7 B (0%)

Total Size: 1.12 MB

Filename	Size	Change
build/block-library/index.js	126 kB	+7 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/api-fetch/index.js	3.4 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	6.48 kB	0 B
build/block-directory/style-rtl.css	787 B	0 B
build/block-directory/style.css	787 B	0 B
build/block-editor/index.js	106 kB	0 B
build/block-editor/style-rtl.css	11.3 kB	0 B
build/block-editor/style.css	11.3 kB	0 B
build/block-library/editor-rtl.css	7.87 kB	0 B
build/block-library/editor.css	7.88 kB	0 B
build/block-library/style-rtl.css	7.69 kB	0 B
build/block-library/style.css	7.68 kB	0 B
build/block-library/theme-rtl.css	684 B	0 B
build/block-library/theme.css	686 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	48.2 kB	0 B
build/components/index.js	190 kB	0 B
build/components/style-rtl.css	19.5 kB	0 B
build/components/style.css	19.5 kB	0 B
build/compose/index.js	9.32 kB	0 B
build/core-data/index.js	11.4 kB	0 B
build/data-controls/index.js	1.29 kB	0 B
build/data/index.js	8.43 kB	0 B
build/date/index.js	5.47 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	568 B	0 B
build/dom/index.js	3.11 kB	0 B
build/edit-navigation/index.js	8.19 kB	0 B
build/edit-navigation/style-rtl.css	857 B	0 B
build/edit-navigation/style.css	856 B	0 B
build/edit-post/index.js	302 kB	0 B
build/edit-post/style-rtl.css	5.43 kB	0 B
build/edit-post/style.css	5.43 kB	0 B
build/edit-site/index.js	14.1 kB	0 B
build/edit-site/style-rtl.css	2.96 kB	0 B
build/edit-site/style.css	2.96 kB	0 B
build/edit-widgets/index.js	8.88 kB	0 B
build/edit-widgets/style-rtl.css	2.4 kB	0 B
build/edit-widgets/style.css	2.4 kB	0 B
build/editor/editor-styles-rtl.css	425 B	0 B
build/editor/editor-styles.css	428 B	0 B
build/editor/index.js	44.6 kB	0 B
build/editor/style-rtl.css	4.26 kB	0 B
build/editor/style.css	4.27 kB	0 B
build/element/index.js	4.64 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	502 B	0 B
build/format-library/style.css	502 B	0 B
build/hooks/index.js	2.13 kB	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/keyboard-shortcuts/index.js	2.51 kB	0 B
build/keycodes/index.js	1.94 kB	0 B
build/list-reusable-blocks/index.js	3.13 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/notices/index.js	1.79 kB	0 B
build/nux/index.js	3.4 kB	0 B
build/nux/style-rtl.css	616 B	0 B
build/nux/style.css	613 B	0 B
build/plugins/index.js	2.56 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	2.85 kB	0 B
build/rich-text/index.js	14.8 kB	0 B
build/server-side-render/index.js	2.68 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/viewport/index.js	1.84 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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