format_signatures: Fix whitespace issues and add tests

[jbms]

No description provided.

[2bndy5]

Would this be better?

Suggested change

	del new_node[:]
	new_node.children.clear()

I think the current change would delete children and attributes, no?

[2bndy5]

Why all the breaks? Seems like a simple return makes sense.

Suggested change

	first_name_text_node: Optional[docutils.nodes.Text] = None
	for adjusted_node in adjusted_nodes:
	node: docutils.nodes.Element
	for node in adjusted_node.findall(
	lambda node: (
	isinstance(node, sphinx.addnodes.desc_addname)
	or (
	isinstance(node, sphinx.addnodes.desc_name)
	and "sig-name-nonprimary" not in node["classes"]
	)
	)
	):
	for text_node in cast(docutils.nodes.Element, node).findall(
	docutils.nodes.Text
	):
	first_name_text_node = text_node
	break
	if first_name_text_node is not None:
	break
	if first_name_text_node is not None:
	break
	return first_name_text_node
	for adjusted_node in adjusted_nodes:
	node: docutils.nodes.Element
	for node in adjusted_node.findall(
	lambda node: (
	isinstance(node, sphinx.addnodes.desc_addname)
	or (
	isinstance(node, sphinx.addnodes.desc_name)
	and "sig-name-nonprimary" not in node["classes"]
	)
	)
	):
	for text_node in cast(docutils.nodes.Element, node).findall(
	docutils.nodes.Text
	):
	return text_node
	return None