Extension registry: add sphinxprettysearchresults to blacklist

[jayaddison]

Feature or Bugfix

• Bugfix

Purpose

• Discourage use of the now-fairly-long-redundant sphinxprettysearchresults extension.

Detail

• Adds sphinxprettysearchresults to the list of blacklisted extensions, with the corresponding Sphinx version where the functionality became available in Sphinx core (v2.0.0).

Relates

• Resolves sphinx-pretty-searchresults is now redundant #11925.
• Relates to HTML Search results aren't reader friendly #1618, #1618 make search results reader friendly #4022.

[jayaddison]

Note for anyone curious / reviewing: adding an extension to the blacklist doesn't prevent a project from building, but it does cause a warning message to be emitted, and the extension will not be loaded.

Relevant code snippet:

sphinx/sphinx/registry.py

Lines 438 to 446 in aff9578

	def load_extension(self, app: Sphinx, extname: str) -> None:
	"""Load a Sphinx extension."""
	if extname in app.extensions: # already loaded
	return
	if extname in EXTENSION_BLACKLIST:
	logger.warning(__('the extension %r was already merged with Sphinx since '
	'version %s; this extension is ignored.'),
	extname, EXTENSION_BLACKLIST[extname])
	return