Fix content resizing "Shorten" action for CJK languages

[i-anubhav-anand]

Problem

Fixes #578

Japanese, Chinese, and Korean text doesn't use spaces as word separators. @wordpress/wordcount's count( text, 'words', {} ) returns near-zero for CJK content, so the "Shorten" action always showed the error "Text is too short to shorten further." even for long paragraphs.

Solution

Detect CJK content via a Unicode range regex and switch to 'characters_excluding_spaces' counting with a character-based minimum threshold (SHORTEN_MIN_CHARS = 10). The same locale-aware counting is applied to the word-diff display so the +/− indicator remains meaningful for CJK text.

Non-CJK content is unaffected — the existing SHORTEN_MIN_WORDS = 5 path runs as before.

Changes

• src/experiments/content-resizing/components/ContentResizingToolbar.tsx
  • Add CJK_REGEX and SHORTEN_MIN_CHARS constants
  • handleAction('shorten'): use characters_excluding_spaces count for CJK content
  • wordDiff memo: use locale-aware count for accurate +/− display

Testing

1. Create a post with Japanese/Chinese/Korean paragraph text (e.g. これはテストです。日本語のコンテンツをテストしています。)
2. Select a text block and open the AI resize menu
3. Click Shorten — it should proceed without the "too short" error
4. Verify the word-diff badge shows a reasonable character delta
5. With English text, verify the existing behaviour is unchanged

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Co-authored-by: i-anubhav-anand <anubhav24@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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[dkotter]

@i-anubhav-anand Thanks for the PR but we do already have an open PR that resolves this same thing (see #581). I'd suggest reviewing that PR and if you have comments or concerns with the approach, best to leave those there instead of opening this duplicate PR.

[i-anubhav-anand]

Thanks @dkotter — you're right, this overlaps the existing PR you linked. Closing in favor of it to keep the work consolidated; happy to help review or iterate there instead. Apologies for the duplicated effort!