[Refactor] Slash-n-Burn HTML BuiltIn XBlock

[irfanuddinahmad]

See parent epic: openedx/openedx-platform#37819

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Rollout Position

Step 4 of 8 — Medium footprint (~1,650 LOC). The HTML block has multiple template variants (raw, iframe, LaTeX, zooming-image, announcement, anon_user_id) — confirm all variants are handled correctly in xblocks-contrib before removing.

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Block Details

Toggle	USE_EXTRACTED_HTML_BLOCK in openedx/envs/common.py
Shim class	_BuiltInHtmlBlock in xmodule/html_block.py
Entrypoint	html = "xmodule.html_block:HtmlBlock" in pyproject.toml

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Checklist

Pre-condition

• Review PRs merged into the built-in HTML XBlock code in edx-platform after the extraction work was done — port any bug fixes or improvements to xblocks-contrib if not already there.
• Confirm all template variants (raw, iframe, LaTeX, zooming-image, announcement, anon_user_id) are supported in xblocks-contrib.

Steps (single PR)

• Remove the toggle — delete USE_EXTRACTED_HTML_BLOCK from openedx/envs/common.py and all usages.
• Remove the shim — delete _BuiltInHtmlBlock class and the from xblocks_contrib.html import HtmlBlock as _ExtractedHtmlBlock import from xmodule/html_block.py.
• Remove the entrypoint — delete html = "xmodule.html_block:HtmlBlock" from pyproject.toml.
• Remove remaining assets:
  • xmodule/html_block.py (Python class)
  • xmodule/html_checker.py
  • xmodule/js/src/html/ (display.js, edit.js, imageModal.js)
  • xmodule/templates/html/ (6 YAML template variants)
  • xmodule/static/css-builtin-blocks/HtmlBlockDisplay.css
  • xmodule/static/css-builtin-blocks/HtmlBlockEditor.css
  • Webpack entries HtmlBlockDisplay / HtmlBlockEditor in webpack.builtinblocks.config.js
• Run smoke tests on the extracted HTML block to verify nothing is broken.

[irfanuddinahmad]

Implementation PR: openedx/openedx-platform#38748