The patching is not required, async def is valid in all supported Python versions. Moves the async/patched sync functions from asyncsupport into the regular code. Moves the async filters from asyncfilters to filters. This does mess with the signature arguments in the docs for the filters, I think that can be fixed in Pallets-Sphinx-Theme's Jinja support.

import asyncio is done inside render and generate to avoid importing it at the top, which would slow down import time.

• fixes remove async patching system #1390

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.