Bug 129558

Currently, in order to provide the default XML navigator for files whose MIME types end in +xml (such as
text/x-springconfig+xml) one has to explicitly register org.netbeans.modules.xml.text.navigator.XMLNavigatorPanel for
that MIME type. The navigator support does not infer to use the navigator for text/xml if a navigator is not registered
for the more specific MIME type. There are quite many files using the +xml suffix, and all of them need to have this
dependency on xml.text.

Ways to address include adding special support to core/navigator for handling the XML MIME types, or providing an API in
xml.text to return the default XML navigator.

However, there is already support in the IDE for infering text/xml from a "+xml" MIME type: the MIME lookup. The
navigator support could either use the editor MIME lookup (over the Editors folder), or have it own MIME lookup over the
current Navigator folder.