Fix HtmlUtils unescape for supplementary chars #35477
                
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Closes: #35426
Currently,
HtmlUtils.htmlUnescape()does not correctly handle numeric character references for Unicode supplementary characters (e.g., emojis).For example, an entity like
😀(😀) is incorrectly converted to a garbled character corresponding toU+F600due to data truncation.Step to Reproduce
Cause
The root cause was a problematic cast to a 16-bit
charin theHtmlCharacterEntityDecoder. This operation truncated any Unicode code point value greater thanU+FFFF, leading to the loss of the most significant bits.Solution
This PR resolves the issue by replacing the direct
(char)cast with a call toStringBuilder.appendCodePoint().The
appendCodePoint()method is designed to handle the full range of Unicode code points. It correctly converts supplementary characters into a two-character surrogate pair, ensuring that all characters are unescaped without data loss. A corresponding unit test has been added to verify this fix.