Code Action to generate elementFormDefault="qualified" from XML

[angelozerr]

This issue #856 fixes the infinite loop error range and server doesn't stop when you try to validate the foo.xml file too many times (because of infinite loop).

But code action is wrong:

After spending time, the correct fix is to add elementFormDefault="qualified" in the XSD file:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
	elementFormDefault="qualified"
	xmlns:xs="http://www.w3.org/2001/XMLSchema"
	targetNamespace="http://foo">
	<xs:element name="foo">
		<xs:complexType>
			<xs:sequence>
				<xs:element name="bar" />
			</xs:sequence>
		</xs:complexType>
	</xs:element>
</xs:schema>

I think it's an hard task.