{{ csrftoken() }} doesn't work with datasette.render_template()

[simonw]

The documentation here suggests that it will work:

datasette/docs/internals.rst

Lines 540 to 546 in eed116a

	Datasette uses `asgi-csrf <https://github.com/simonw/asgi-csrf>`__ to guard against CSRF attacks on form POST submissions. Users receive a ``ds_csrftoken`` cookie which is compared against the ``csrftoken`` form field (or ``x-csrftoken`` HTTP header) for every incoming request.
	If your plugin implements a ``<form method="POST">`` anywhere you will need to include that token. You can do so with the following template snippet:
	.. code-block:: html
	<input type="hidden" name="csrftoken" value="{{ csrftoken() }}">

But right now the csrftoken variable is set in BaseView.render, which means it's not visible to plugins that try to render templates using datasette.render_template:

datasette/datasette/views/base.py

Lines 99 to 106 in 799c5d5

	async def render(self, templates, request, context=None):
	context = context or {}
	template = self.ds.jinja_env.select_template(templates)
	template_context = {
	**context,
	**{
	"database_url": self.database_url,
	"csrftoken": request.scope["csrftoken"],