stddoclet: Want to distinguish whether external link is to class or interface

When Javadoc uses -link to link to another set D of documentation, it currently
uses package-list for D to determine if a class or interface is documented
there. This works fine, but does not inform Javadoc as to whether it is
a class or interface. This information could then be used to make
the interface name italic, and to describe in its link's tooltip whether
it is a class or interface, as described in RFE 4714257 "Add description
that italics means interface for accessibility."

If Javadoc generated a class-list as follows, this would be possible:

com.package1.Class1 class
com,package1.Class2 class
com.package1.Interface1 interface

or

class com.package1.Class1
class com,package1.Class2
interface com.package1.Interface1

or use the same XML elements used in XML Doclet:

<class type="class"> com.package1.Class1 </class>
<class type="class"> com.package1.Class2 </class>
<class type="interface"> com.package1.Interface1 </class>

or use the style from the XML book file of the MIF Doclet:

<class> com.package1.Class1 </class>
<class> com.package1.Class2 </class>
<interface> com.package1.Interface1 </interface>

This last one seems the cleanest.

Perhaps there might be other benefits in having this list.