Rich text: fix soft line break in caption on enter

[ellatrix]

Description

Fixes #23574.

Recently we introduced splitting of a caption when the caret is at then end of a caption, but accidentally removed the ability to insert soft line breaks elsewhere. This PR reintroduces that.

To do: add an e2e test.

How has this been tested?

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: -11 B (0%)

Total Size: 1.13 MB

Filename	Size	Change
build/block-editor/index.js	109 kB	-11 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
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build/annotations/index.js	3.62 kB	0 B
build/api-fetch/index.js	3.4 kB	0 B
build/autop/index.js	2.82 kB	0 B
build/blob/index.js	620 B	0 B
build/block-directory/index.js	7.42 kB	0 B
build/block-directory/style-rtl.css	941 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-editor/style-rtl.css	10.7 kB	0 B
build/block-editor/style.css	10.7 kB	0 B
build/block-library/editor-rtl.css	7.63 kB	0 B
build/block-library/editor.css	7.63 kB	0 B
build/block-library/index.js	129 kB	0 B
build/block-library/style-rtl.css	7.79 kB	0 B
build/block-library/style.css	7.79 kB	0 B
build/block-library/theme-rtl.css	730 B	0 B
build/block-library/theme.css	732 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	198 kB	0 B
build/components/style-rtl.css	15.9 kB	0 B
build/components/style.css	15.8 kB	0 B
build/compose/index.js	9.65 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	8.45 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	569 B	0 B
build/dom/index.js	3.19 kB	0 B
build/edit-navigation/index.js	9.88 kB	0 B
build/edit-navigation/style-rtl.css	1.02 kB	0 B
build/edit-navigation/style.css	1.02 kB	0 B
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build/edit-post/style-rtl.css	5.54 kB	0 B
build/edit-post/style.css	5.54 kB	0 B
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build/edit-widgets/style.css	2.42 kB	0 B
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build/editor/style.css	3.82 kB	0 B
build/element/index.js	4.65 kB	0 B
build/escape-html/index.js	733 B	0 B
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build/format-library/style-rtl.css	547 B	0 B
build/format-library/style.css	548 B	0 B
build/hooks/index.js	2.13 kB	0 B
build/html-entities/index.js	622 B	0 B
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build/is-shallow-equal/index.js	710 B	0 B
build/keyboard-shortcuts/index.js	2.51 kB	0 B
build/keycodes/index.js	1.94 kB	0 B
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build/list-reusable-blocks/style-rtl.css	450 B	0 B
build/list-reusable-blocks/style.css	451 B	0 B
build/media-utils/index.js	5.3 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	671 B	0 B
build/nux/style.css	668 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	788 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/rich-text/index.js	14 kB	0 B
build/server-side-render/index.js	2.68 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	4.06 kB	0 B
build/viewport/index.js	1.85 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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