HTML API: Preserve raw text contents in serialize

[sirreal]

IFRAME, NOEMBED, and NOFRAMES contents were omitted from normalized HTML. Print their rawtext contents verbatim according to the standard for serializing HTML fragments.

If current node is a Text node
If the parent of current node is a style, script, xmp, iframe, noembed, noframes, or plaintext element, or if the parent of current node is a noscript element and scripting is enabled for the node, then append the value of current node's data literally.

Otherwise, append the value of current node's data, escaped as described below.

Trac ticket: https://core.trac.wordpress.org/ticket/65372

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5.5
Used for: Detection and initial implementation.

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[github-actions]

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