Treat U+3000 and U+FF5E as CJK punctuation-equivalent in Markdown prose wrap (#18656)

Co-authored-by: fisker <lionkay@gmail.com>

changelog_unreleased/javascript/18594.md

@@ -2,12 +2,13 @@
 
 Some tools treat these spaces as meaningful.
 
-```bash
-await require('prettier').format('/**\n * With 2 spaces   \n */', {parser: 'babel'});
+```js
+await prettier.format("/**\n * With 2 spaces   \n */", { parser: "babel" });
 
-# Prettier stable
+/* Prettier stable */
 // -> '/**\n * With 2 spaces\n */\n'
 
-# Prettier main
+/* Prettier main */
 // -> '/**\n * With 2 spaces  \n */\n'
+//                          ^^ space preserved
 ```

changelog_unreleased/markdown/18656.md

@@ -0,0 +1,17 @@
+#### Treat U+3000 as CJK punctuation-equivalent and make sure to recognize U+FF5E as CJK punctuation again in Markdown prose wrap (#18656 by @tats-u)
+
+We improved the text wrapping in Markdown written in Chinese and Japanese by treating some non Unicode punctuation characters as equivalent to CJK punctuation. A part of this was assumed to have been introduced in 3.5.0 ([#16832](https://github.com/prettier/prettier/pull/16832)), but it was not fully implemented and not noticed until now due to insufficient test cases.
+
+```js
+await prettier.format(
+  "U+3000\u{3000}\nU+301C\u{301C}\nU+FF5E\u{FF5E}\nU+1F221\u{1F221} 测试 Test テスト\n",
+  { parser: "markdown", proseWrap: "always" },
+);
+
+/* Prettier stable */
+// -> 'U+3000　 U+301C〜U+FF5E～ U+1F221🈡 测试 Test テスト\n'
+//           　^ extra space  　^ extra space
+
+/* Prettier main */
+// -> 'U+3000　U+301C〜U+FF5E～U+1F221🈡 测试 Test テスト\n'
+```