Add support for textDocument/typeDefinition from XML to XMLSchema/DTD

[angelozerr]

When XML file is bound to an XML Schema or DTD it should be cool to manage type definition inside XML to open the XML Schema (element or attribute) / DTD element/attrlist which defines the XML element/attribute.

Take a sample with this xml:

<book isbn="0836217462" xmlns="http://example.org/ns/books/">
   <title>bla bla bla</title>
</book>

bound to this XML Schema:

<xsd:element name="book">
 <xsd:complexType>
  <xsd:sequence>
   <xsd:element name="title" type="xsd:string"/>
   <xsd:attribute name="isbn" type="xsd:string"/>
  </xsd:sequence>
 </xsd:complexType>
</xsd:element>

• when type definition is done in the xml attribute book/@isbn it should open the XML Schema and select the value of @name of <xsd:attribute name="isbn" (isbn).

• when type definition is done in the xml elementbook/title it should open the XML Schema and select the value of @name of <xsd:element name="title" (title).

Same thing should be done for XML bound to DTD