Mark the built-in blocks deprecated

[farhan]

• Update enabled extracted block feature flag docs
• Add deprecated warning to the enabled built-in blocks

[kdmccormick]

thanks for opening this!

[kdmccormick]

This would be very noisy--we'd get a log entry every time the block was constructed, which could be multiple times per request. How about putting it at the top-level of the module, within if not settings.USE_EXTRACTED_VIDEO_BLOCK: ? That way it'll show once at startup.

I would also recommend mentioning the setting name and that it will be removed in Verawood. When an operator sees warnings in their logs, the questions they will have are "how can I fix this?" and "how long do I have to fix it?"

[kdmccormick]

Perfect 💯

I tested the warnings with built-in LTI and extracted HTML:

In [1]: from xblock.core import XBlock ; XBlock.load_class("lti")
2026-03-17 14:36:48,443 WARNING 39 [py.warnings] [user None] [ip None] warnings.py:112 - /opt/pyenv/versions/3.12.12/lib/python3.12/importlib/__init__.py:90: DeprecationWarning: The built-in `xmodule.lti_block` LTIBlock implementation is deprecated. To fix this warning, enable `USE_EXTRACTED_LTI_BLOCK` (set it to True) to use `xblocks_contrib.lti.LTIBlock` instead. Support for the built-in implementation, and the `USE_EXTRACTED_LTI_BLOCK` setting, will be removed in Willow.
  return _bootstrap._gcd_import(name[level:], package, level)
Out[1]: xmodule.lti_block._BuiltInLTIBlock

In [2]: from xblock.core import XBlock ; XBlock.load_class("html")
Out[2]: xblocks_contrib.html.html.HtmlBlock