Description

The safest part of #15081

Prettier removes non-ASCII whitespaces at the end of the line and beginning of the next line in Markdown, which violates the CommonMark spec.

The space (U+3000) in the following should be kept:

# 例

　全角スペース全形空白

https://spec.commonmark.org/0.31.2/#soft-line-breaks

Spaces at the end of the line and beginning of the next line are removed:

https://spec.commonmark.org/0.31.2/#unicode-whitespace-character

A Unicode whitespace character is a character in the Unicode Zs general category, or a tab (U+0009), line feed (U+000A), form feed (U+000C), or carriage return (U+000D).

Unicode whitespace is a sequence of one or more Unicode whitespace characters.

A space is U+0020.

The CommonMark spec doesn't mention non-ASCII spaces here, so they should be reserved.

Checklist

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory).
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

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