Completion for prefix of attribute name

[dev-bz]

When editing a XML file, the tag name have complete with prefix but attribute name is missing its prefix. Pls make it better.

<!-- other.xsd -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="test-attrs">
	<xs:attribute name="label" type="xs:string"/>
</xs:schema>
<!-- sample.xsd -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:test="test-attrs">
	<xs:import schemaLocation="other.xsd" namespace="test-attrs"/>
	<xs:element name="sample">
		<xs:complexType>
		<xs:attribute ref="test:label"/>
		</xs:complexType>
	</xs:element>
</xs:schema>
<!-- sample.xml (✘error version) -->
<sample xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:test="test-attrs" xsi:noNamespaceSchemaLocation="sample.xsd"
	label="sample"/>
<!-- sample.xml (✔correct version) -->
<sample xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:test="test-attrs" xsi:noNamespaceSchemaLocation="sample.xsd"
	test:label="sample"/>

[angelozerr]

@dev-bz I'm fixing your issue, see demo at #1191 (comment)